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Cx43 hemichannels and panx1 channels contribute to ethanol-induced astrocyte dysfunction and damage

Alcohol, a widely abused drug, significantly diminishes life quality, causing chronic diseases and psychiatric issues, with severe health, societal, and economic repercussions. Previously, we demonstrated that...

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Galectins in epithelial-mesenchymal transition: roles and mechanisms contributing to tissue repair, fibrosis and cancer metastasis

Galectins are soluble glycan-binding proteins that interact with a wide range of glycoproteins and glycolipids and modulate a broad spectrum of physiological and pathological processes. The expression and subc...

Glutaminolysis regulates endometrial fibrosis in intrauterine adhesion via modulating mitochondrial function

Endometrial fibrosis, a significant characteristic of intrauterine adhesion (IUA), is caused by the excessive differentiation and activation of endometrial stromal cells (ESCs). Glutaminolysis is the metabolic...

The long-chain flavodoxin FldX1 improves the biodegradation of 4-hydroxyphenylacetate and 3-hydroxyphenylacetate and counteracts the oxidative stress associated to aromatic catabolism in Paraburkholderia xenovorans

Bacterial aromatic degradation may cause oxidative stress. The long-chain flavodoxin FldX1 of Paraburkholderia xenovorans LB400 counteracts reactive oxygen species (ROS). The aim of this study was to evaluate the...

MicroRNA-148b secreted by bovine oviductal extracellular vesicles enhance embryo quality through BPM/TGF-beta pathway

Extracellular vesicles (EVs) and their cargoes, including MicroRNAs (miRNAs) play a crucial role in cell-to-cell communication. We previously demonstrated the upregulation of bta-mir-148b in EVs from oviductal...

YME1L-mediated mitophagy protects renal tubular cells against cellular senescence under diabetic conditions

The senescence of renal tubular epithelial cells (RTECs) is crucial in the progression of diabetic kidney disease (DKD). Accumulating evidence suggests a close association between insufficient mitophagy and RT...

Effects of latroeggtoxin-VI on dopamine and α-synuclein in PC12 cells and the implications for Parkinson’s disease

Parkinson’s disease (PD) is characterized by death of dopaminergic neurons leading to dopamine deficiency, excessive α-synuclein facilitating Lewy body formation, etc. Latroeggtoxin-VI (LETX-VI), a proteinaceo...

Glial-restricted progenitor cells: a cure for diseased brain?

The central nervous system (CNS) is home to neuronal and glial cells. Traditionally, glia was disregarded as just the structural support across the brain and spinal cord, in striking contrast to neurons, alway...

Carbapenem-resistant hypervirulent ST23 Klebsiella pneumoniae with a highly transmissible dual-carbapenemase plasmid in Chile

The convergence of hypervirulence and carbapenem resistance in the bacterial pathogen Klebsiella pneumoniae represents a critical global health concern. Hypervirulent K. pneumoniae (hvKp) strains, frequently from...

Endometrial mesenchymal stromal/stem cells improve regeneration of injured endometrium in mice

The monthly regeneration of human endometrial tissue is maintained by the presence of human endometrial mesenchymal stromal/stem cells (eMSC), a cell population co-expressing the perivascular markers CD140b an...

Embryo development is impaired by sperm mitochondrial-derived ROS

Basal energetic metabolism in sperm, particularly oxidative phosphorylation, is known to condition not only their oocyte fertilising ability, but also the subsequent embryo development. While the molecular pat...

Fibroblasts inhibit osteogenesis by regulating nuclear-cytoplasmic shuttling of YAP in mesenchymal stem cells and secreting DKK1

Fibrous scars frequently form at the sites of bone nonunion when attempts to repair bone fractures have failed. However, the detailed mechanism by which fibroblasts, which are the main components of fibrous sc...

MSC-derived exosomes protect auditory hair cells from neomycin-induced damage via autophagy regulation

Sensorineural hearing loss (SNHL) poses a major threat to both physical and mental health; however, there is still a lack of effective drugs to treat the disease. Recently, novel biological therapies, such as ...

Alpha-synuclein dynamics bridge Type-I Interferon response and SARS-CoV-2 replication in peripheral cells

Increasing evidence suggests a double-faceted role of alpha-synuclein (α-syn) following infection by a variety of viruses, including SARS-CoV-2. Although α-syn accumulation is known to contribute to cell toxic...

Lactadherin immunoblockade in small extracellular vesicles inhibits sEV-mediated increase of pro-metastatic capacities

Tumor-derived small extracellular vesicles (sEVs) can promote tumorigenic and metastatic capacities in less aggressive recipient cells mainly through the biomolecules in their cargo. However, despite recent ad...

Integration of ATAC-seq and RNA-seq identifies MX1-mediated AP-1 transcriptional regulation as a therapeutic target for Down syndrome

Growing evidence has suggested that Type I Interferon (I-IFN) plays a potential role in the pathogenesis of Down Syndrome (DS). This work investigates the underlying function of MX1, an effector gene of I-IFN,...

The novel roles of YULINK in the migration, proliferation and glycolysis of pulmonary arterial smooth muscle cells: implications for pulmonary arterial hypertension

Abnormal remodeling of the pulmonary vasculature, characterized by the proliferation and migration of pulmonary arterial smooth muscle cells (PASMCs) along with dysregulated glycolysis, is a pathognomonic feat...

Electroacupuncture promotes neurogenesis in the dentate gyrus and improves pattern separation in an early Alzheimer's disease mouse model

Impaired pattern separation occurs in the early stage of Alzheimer’s disease (AD), and hippocampal dentate gyrus (DG) neurogenesis participates in pattern separation. Here, we investigated whether spatial memo...

Role of SYVN1 in the control of airway remodeling in asthma protection by promoting SIRT2 ubiquitination and degradation

Asthma is a heterogenous disease that characterized by airway remodeling. SYVN1 (Synoviolin 1) acts as an E3 ligase to mediate the suppression of endoplasmic reticulum (ER) stress through ubiquitination and de...

Advances towards the use of gastrointestinal tumor patient-derived organoids as a therapeutic decision-making tool

In December 2022 the US Food and Drug Administration (FDA) removed the requirement that drugs in development must undergo animal testing before clinical evaluation, a declaration that now demands the establish...

Melatonin alleviates pyroptosis by regulating the SIRT3/FOXO3α/ROS axis and interacting with apoptosis in Atherosclerosis progression

Atherosclerosis (AS), a significant contributor to cardiovascular disease (CVD), is steadily rising with the aging of the global population. Pyroptosis and apoptosis, both caspase-mediated cell death mechanism...

Prenatal ethanol exposure and changes in fetal neuroendocrine metabolic programming

Prenatal ethanol exposure (PEE) (mainly through maternal alcohol consumption) has become widespread. However, studies suggest that it can cause intrauterine growth retardation (IUGR) and multi-organ developmen...

Autologous non-invasively derived stem cells mitochondria transfer shows therapeutic advantages in human embryo quality rescue

The decline in the quantity and quality of mitochondria are closely associated with infertility, particularly in advanced maternal age. Transferring autologous mitochondria into the oocytes of infertile female...

Development of synthetic modulator enabling long-term propagation and neurogenesis of human embryonic stem cell-derived neural progenitor cells

Neural progenitor cells (NPCs) are essential for in vitro drug screening and cell-based therapies for brain-related disorders, necessitating well-defined and reproducible culture systems. Current strategies em...

Heat-responsive microRNAs participate in regulating the pollen fertility stability of CMS-D2 restorer line under high-temperature stress

Anther development and pollen fertility of cytoplasmic male sterility (CMS) conditioned by Gossypium harknessii cytoplasm (CMS-D2) restorer lines are susceptible to continuous high-temperature (HT) stress in sum...

Chemogenetic inhibition of NTS astrocytes normalizes cardiac autonomic control and ameliorate hypertension during chronic intermittent hypoxia

Obstructive sleep apnea (OSA) is characterized by recurrent episodes of chronic intermittent hypoxia (CIH), which has been linked to the development of sympathoexcitation and hypertension. Furthermore, it has ...

SARS-CoV-2 spike protein S1 activates Cx43 hemichannels and disturbs intracellular Ca 2+ dynamics

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes the ongoing coronavirus disease 2019 (COVID-19). An aspect of high uncertainty is whether the SARS-CoV-2 per se or the systemic inflammation ...

The effect of zofenopril on the cardiovascular system of spontaneously hypertensive rats treated with the ACE2 inhibitor MLN-4760

Angiotensin converting enzyme 2 (ACE2) plays a crucial role in the infection cycle of SARS-CoV-2 responsible for formation of COVID-19 pandemic. In the cardiovascular system, the virus enters the cells by bind...

Two murine models of sepsis: immunopathological differences between the sexes—possible role of TGFβ1 in female resistance to endotoxemia

Endotoxic shock (ExSh) and cecal ligature and puncture (CLP) are models that induce sepsis. In this work, we investigated early immunologic and histopathologic changes induced by ExSh or CLP models in female a...

An intracellular, non-oxidative factor activates in vitro chromatin fragmentation in pig sperm

In vitro incubation of epididymal and vas deferens sperm with Mn 2+ induces Sperm Chromatin Fragmentation (SCF), a mechanism that causes double-stranded breaks in toroid-linker regions (TLRs). Whether this mechani...

Focal ischemic stroke modifies microglia-derived exosomal miRNAs: potential role of mir-212-5p in neuronal protection and functional recovery

Ischemic stroke is a severe type of stroke with high disability and mortality rates. In recent years, microglial exosome-derived miRNAs have been shown to be promising candidates for the treatment of ischemic ...

S -Nitrosylation in endothelial cells contributes to tumor cell adhesion and extravasation during breast cancer metastasis

Nitric oxide is produced by different nitric oxide synthases isoforms. NO activates two signaling pathways, one dependent on soluble guanylate cyclase and protein kinase G, and other where NO post-translationa...

Identifying pyroptosis- and inflammation-related genes in intracranial aneurysms based on bioinformatics analysis

Intracranial aneurysm (IA) is the most common cerebrovascular disease, and subarachnoid hemorrhage caused by its rupture can seriously impede nerve function. Pyroptosis is an inflammatory mode of cell death wh...

Drosophila Atlastin regulates synaptic vesicle mobilization independent of bone morphogenetic protein signaling

The endoplasmic reticulum (ER) contacts endosomes in all parts of a motor neuron, including the axon and presynaptic terminal, to move structural proteins, proteins that send signals, and lipids over long dist...

Mucin1 induced trophoblast dysfunction in gestational diabetes mellitus via Wnt/β-catenin pathway

To elucidate the role of Mucin1 (MUC1) in the trophoblast function (glucose uptake and apoptosis) of gestational diabetes mellitus (GDM) women through the Wnt/β-catenin pathway.

Human umbilical cord mesenchymal stem cells (hUC-MSCs) alleviate paclitaxel-induced spermatogenesis defects and maintain male fertility

Chemotherapeutic drugs can cause reproductive damage by affecting sperm quality and other aspects of male fertility. Stem cells are thought to alleviate the damage caused by chemotherapy drugs and to play role...

Exploring the Neandertal legacy of pancreatic ductal adenocarcinoma risk in Eurasians

The genomes of present-day non-Africans are composed of 1–3% of Neandertal-derived DNA as a consequence of admixture events between Neandertals and anatomically modern humans about 50–60 thousand years ago. Ne...

Identification and analysis of key hypoxia- and immune-related genes in hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM), an autosomal dominant genetic disease, is the main cause of sudden death in adolescents and athletes globally. Hypoxia and immune factors have been revealed to be related to ...

How do prolonged anchorage-free lifetimes strengthen non-small-cell lung cancer cells to evade anoikis? – A link with altered cellular metabolomics

Malignant cells adopt anoikis resistance to survive anchorage-free stresses and initiate cancer metastasis. It is still unknown how varying periods of anchorage loss contribute to anoikis resistance, cell migr...

Single nucleotide polymorphisms associated with wine fermentation and adaptation to nitrogen limitation in wild and domesticated yeast strains

For more than 20 years, Saccharomyces cerevisiae has served as a model organism for genetic studies and molecular biology, as well as a platform for biotechnology (e.g., wine production). One of the important eco...

Investigating the dark-side of the genome: a barrier to human disease variant discovery?

The human genome contains regions that cannot be adequately assembled or aligned using next generation short-read sequencing technologies. More than 2500 genes are known contain such ‘dark’ regions. In this st...

Hyperbaric oxygen treatment increases intestinal stem cell proliferation through the mTORC1/S6K1 signaling pathway in Mus musculus

Hyperbaric oxygen treatment (HBOT) has been reported to modulate the proliferation of neural and mesenchymal stem cell populations, but the molecular mechanisms underlying these effects are not completely unde...

Polar microalgae extracts protect human HaCaT keratinocytes from damaging stimuli and ameliorate psoriatic skin inflammation in mice

Polar microalgae contain unique compounds that enable them to adapt to extreme environments. As the skin barrier is our first line of defense against external threats, polar microalgae extracts may possess res...

Correction: Utility of melatonin in mitigating ionizing radiation‑induced testis injury through synergistic interdependence of its biological properties

The original article was published in Biological Research 2022 55 :33

Beyond energy provider: multifunction of lipid droplets in embryonic development

Since the discovery, lipid droplets (LDs) have been recognized to be sites of cellular energy reserves, providing energy when necessary to sustain cellular life activities. Many studies have reported large num...

Retraction Note: Tridax procumbens flavonoids: a prospective bioactive compound increased osteoblast differentiation and trabecular bone formation

Electroacupuncture protective effects after cerebral ischemia are mediated through mir-219a inhibition.

Electroacupuncture (EA) is a complementary and alternative therapy which has shown protective effects on vascular cognitive impairment (VCI). However, the underlying mechanisms are not entirely understood.

Topsoil and subsoil bacterial community assemblies across different drainage conditions in a mountain environment

High mountainous environments are of particular interest as they play an essential role for life and human societies, while being environments which are highly vulnerable to climate change and land use intensi...

Functional defects in hiPSCs-derived cardiomyocytes from patients with a PLEKHM2-mutation associated with dilated cardiomyopathy and left ventricular non-compaction

Dilated cardiomyopathy (DCM) is a primary myocardial disease, leading to heart failure and excessive risk of sudden cardiac death with rather poorly understood pathophysiology. In 2015, Parvari's group ident...

Human VDAC pseudogenes: an emerging role for VDAC1P8 pseudogene in acute myeloid leukemia

Voltage-dependent anion selective channels (VDACs) are the most abundant mitochondrial outer membrane proteins, encoded in mammals by three genes, VDAC1 , 2 and 3 , mostly ubiquitously expressed. As 'mitochondrial ...

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Biological Research

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Plos biology article types.

PLOS Biology considers works of exceptional significance, originality, and relevance in all areas of biological science, including both primary research, meta-analyses and Magazine articles . Our publication options are outlined below.

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PLOS Biology publishes seven different types of research reports. All research articles are compatible with our easy, format-free submission process, and offer options for preprints, published peer review history, and publishing uncorrected proofs. Most, with rare exception, are also protected by our scooping policy , ensuring that your research will not be rejected for novelty within six-months of the publication of a complementary or confirmatory research publication. We evaluate all research based on the important questions it answers and its potential to impact an international scientific community as well as educators, policy makers, patient advocacy groups, and society more broadly.

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Editorials are written in-house by members of the editorial staff or by members of the Editorial Board.

Perspectives

The Perspectives section provides experts with a forum to comment on topical or controversial issues of broad interest. They address controversial issues or those at the interface between science and policy or science and society; present a policy position aimed at influencing policy decisions; examine and make recommendations on scientific and publishing practices. These are meant to be short, opinionated, Op-ed type of pieces.

The ideal Perspective conveys a sense of urgency. Some things to think about would be:

• Is this topic of immediate concern?
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Controversial articles are welcomed, but the text should acknowledge that a position is in fact controversial and provide readers with enough background on the differing views.

Our Perspectives aim to engage a broad and diverse audience—it is therefore important to ensure that they are written in an accessible, persuasive, and stimulating style that appeals to both specialists and non-specialist readers. Perspectives are usually assessed in-house with our Editorial Board, but we reserve the right to peer-review them if needed. Commissioning does not guarantee publication. Editors work closely with authors to ensure that articles are written in an engaging, succinct, yet rigorous manner.

Guidelines for a Perspective

Example perspectives.

Lowe-Power T, Dyson L, Polter AM (2021) A generation of junior faculty is at risk from the impacts of COVID-19. PLoS Biol 19(5): e3001266. https://doi.org/10.1371/journal.pbio.3001266

Bourne PE (2021) Is “bioinformatics” dead? PLoS Biol 19(3): e3001165. https://doi.org/10.1371/journal.pbio.3001165

Primers provide concise and accessible context to a PLOS Biology research article of broad and current interest. Primers are commissioned and published alongside a research article that would benefit from additional context and/or explanation.

Above all, Primers should demystify an area of biology, avoid and/or explain technical jargon and provide critical and forward-thinking analysis about how the research article fits into the current state of the field and its future. A good Primer will briefly discuss (but not exhaustively review) what we know and what questions we have yet to answer for a particular field. It will then introduce the new findings and describe in roughly three paragraphs the advance represented in the related research article, highlighting its significance, not only for the discipline in question, but across disciplines. The Primer should then explain what the findings suggest in terms of next steps: what new avenues of investigation are opened, what new experiments can be tried, what new ideas can now be tested going forward? Ideally, Primers also offer insight into what big questions are likely to remain unanswered for many years (for whatever reasons).

We encourage the use of a figure to illustrate key concepts/mechanism/conclusions in an informative, easy-to-understand manner.

Primers are usually assessed by our Editorial Board, but we reserve the right to peer-review externally if needed. Commissioning does not guarantee publication. Editors work closely with authors to ensure that articles are written in an engaging, succinct, yet rigorous manner.

Guidelines for a Primer

Example primer.

Kazanova A, Rudd CE (2021) Programmed cell death 1 ligand (PD-L1) on T cells generates Treg suppression from memory. PLoS Biol 19(5): e3001272. https://doi.org/10.1371/journal.pbio.3001272

Guizetti J, Frischknecht F (2021) Apicomplexans: A conoid ring unites them all. PLoS Biol 19(3): e3001105. https://doi.org/10.1371/journal.pbio.3001105

Community Pages

Community Pages provide individuals, networks and organizations with the opportunity to highlight resources, tools, or initiatives of benefit to the scientific community and beyond (including science education and public engagement in science). All resources or tools, and the outputs of initiatives must be open and accessible to all.

Contributors must resist the temptation of self-promotion and instead focus on conveying information to a diverse audience.Community Pages should be written in a succinct, accessible, semi-journalistic style that captures the interest of both specialists and non-specialist readers. We encourage the use of 1-2 figures to illustrate key concepts in an informative, easy to grasp manner; or the use of text boxes for background, self-contained information.

Community Pages are peer-reviewed and commissioning does not guarantee publication. Editors work closely with authors to ensure that articles are written in an engaging, succinct, yet rigorous manner.

Guidelines for a Community Page

Example Community Pages

Weissgerber TL (2021) Training early career researchers to use meta-research to improve science: A participant-guided “learn by doing” approach. PLoS Biol 19(2): e3001073. https://doi.org/10.1371/journal.pbio.3001073

McCullagh EA, Nowak K, Pogoriler A, Metcalf JL, Zaringhalam M, Zelikova TJ (2019) Request a woman scientist: A database for diversifying the public face of science. PLoS Biol 17 (4): e3000212. https://doi.org/10.1371/journal. pbio.3000212

Formal Comments

Formal Comments are intended to provide a formal outlet for the discussion and interpretation of research findings associated with specific articles published in PLOS Biology . They are designed to ensure that readers obtain a balanced view of a scientific or meta-scientific/policy question, especially in areas of debate/controversy. Formal Comments are peer-reviewed and indexed in PubMed.

Formal Comments must be coherent, concise, and well-argued, and are subject to the PLOS Biology criteria for publication . Editors will, as a matter of course, invite the authors of the original article to submit a response to the Formal Comment. Any revisions (of the Formal Comment or the response) will be shared with the authors of the associated comment.

Guidelines for Formal Comments

Example formal comment.

Rees WE, Wackernagel M (2013) The Shoe Fits, but the Footprint is Larger than Earth. PLoS Biol 11(11): e1001701. https://doi.org/10.1371/journal.pbio.1001701​ ​

Example Formal Comment - Response

Blomqvist L, Brook BW, Ellis EC, Kareiva PM, Nordhaus T, Shellenberger M (2013) The Ecological Footprint Remains a Misleading Metric of Global Sustainability. PLoS Biol 11(11): e1001702. https://doi.org/10.1371/journal.pbio.1001702

In-Depth Analysis

Essays are opinionated articles on a topic of interest to scientists and to a broader audience, including the general public. Unlike traditional review articles, which include a comprehensive account of a field, Essays take an imaginative approach to a provocative question, with an engaging but rigorous investigation of the problem. We encourage authors of Essays to select the most representative references to convey their points and avoid exhaustively covering the relevant literature.

The remit of Essays is very broad. They might:

• take stock of progress in a field from a personal point of view
• explore the implications of recent advances that promise to have broad-ranging consequences on a field
• comment on a topical or controversial area of research
• discuss key ideas or educational strategies to enhance understanding of fundamental biological questions
• offer historical/philosophical reflections on contemporary biology
• analyze scientific issues with policy implications

Our Essays aim to engage a broad and diverse audience—it is therefore important to ensure that they are written in an accessible, semi-journalistic style that captures the interest of both specialists and non-specialist readers. We encourage the use of figures to illustrate key concepts in an informative, easy to grasp manner; as well as the use of text boxes for background, self-contained information.

Essays are peer-reviewed and commissioning does not guarantee publication.

Guidelines for an Essay

Example essays.

Rees T, Bosch T, Douglas AE (2018) How the microbiome challenges our concept of self. PLoS Biol 16(2): e2005358. https://doi.org/10.1371/journal.pbio.2005358 Konig C, Weigelt P, Schrader J, Taylor A, Kattge J, Kreft H (2019) Biodiversity data integration—the significance of data resolution and domain. PLoS Biol 17(3): e3000183. https://doi.org/10.1371/journal.pbio.3000183

Unsolved Mysteries

Unsolved Mysteries discuss a topic of biological or medical importance that is poorly understood and in need of research attention—e.g., an unexplored or challenging question, an emerging opportunity, or a recent puzzling phenomenon. The articles are intended to stimulate the scientific community to think about future research possibilities outside their areas of expertise. The articles should be aimed at a very broad audience of biologists—an unsolved mystery in a neuroscience topic should be accessible to ecologists and biophysicists, for example.   The article should include a discussion of the basic science relevant to the topic, why it is biologically or medically important, what work has been done on the topic (if any), major challenges to understanding the question at hand, competing hypotheses, and what advances would be necessary to shed light on the problem. Ideally the structure of the article should reflect the mystery (e.g. subsections with questions as headings). The article should end with a discussion of possible means to a solution

Unsolved Mysteries are peer-reviewed and commissioning does not guarantee publication. Editors work closely with authors to ensure that articles are written in an engaging, succinct, yet rigorous manner.

Guidelines for an Unsolved Mystery

Example unsolved mysteries.

Margolis L, Sadovsky Y (2019) The biology of extracellular vesicles: The known unknowns. PLoS Biol 17(7): e3000363. https://doi.org/10.1371/journal.pbio.3000363

Vogels CBF, Ru¨ckert C, Cavany SM, Perkins TA, Ebel GD, Grubaugh ND (2019) Arbovirus coinfection and co-transmission: A neglected public health concern? PLoS Biol 17(1): e3000130. https://doi.org/10.1371/journal.pbio.3000130

Consensus View

Consensus View articles present a comprehensive analysis by an independent and usually multidisciplinary panel of experts who make specific recommendations on important scientific, publishing or policy issues.

Consensus Views are peer-reviewed and commissioning does not guarantee publication. Editors work closely with authors to ensure that articles are written in an engaging, succinct, yet rigorous manner.

Guidelines for a Consensus View

Example consensus view.

Brown TM, Brainard GC, Cajochen C, Czeisler CA, Hanifin JP, Lockley SW, et al. (2022) Recommendations for daytime, evening, and nighttime indoor light exposure to best support physiology, sleep, and wakefulness in healthy adults. PLoS Biol 20(3): e3001571. https://doi.org/10.1371/journal.pbio.3001571

Kent BA, Holman C, Amoako E, Antonietti A, Azam JM, Ballhausen H, et al. (2022) Recommendations for empowering early career researchers to improve research culture and practice. PLoS Biol 20(7): e3001680. https://doi.org/10.1371/journal.pbio.3001680

Vimercati G, Probert AF, Volery L, Bernardo-Madrid R, Bertolino S, Céspedes V, et al. (2022) The EICAT+ framework enables classification of positive impacts of alien taxa on native biodiversity. PLoS Biol 20(8): e3001729. https://doi.org/10.1371/journal.pbio.3001729

Retired Article Types

Book Review/Science in the Media. These short reviews critiqued books, films, plays, and other media that deal with some aspect of the biological sciences.  

• Education. Although we no longer publish Education articles as a separate article type, we continue publishing them as part of the Education Series. The format selected (Essay, Perspective, or Community Page) depends on the aims of each article.
• Historical and Philosophical Perspectives. The Historical and Philosophical Perspectives section provided professional historians and philosophers of science with a forum to reflect on topical issues in contemporary biology.
• Obituaries.
• Open Highlights. Written in-house by members of the editorial staff, Open Highlights used recent publication as keystones around which to nucleate a short synthesis of several related research articles from PLOS and the wider Open Access corpus.
• Research Matters. Brief pieces by leading scientists explaining why the research carried out in their laboratories - and those of their collaborators and their colleagues - matters to lay audiences. 
• Series. Series were recurrent themed articles on specific topics, including Education, Public Engagement with Science, Cool Tools, and Where Next?
• Synopses. Selected PLOS Biology research articles are accompanied by a synopsis written for a general audience to provide non-experts with insight into the significance of the published work. They are commissioned only.

Post-Publication Notices

PLOS publishes Editorial Notes, Corrections, Expressions of Concern, and Retraction notices, as needed, to address issues that arise after a PLOS article has been published.

Journal of Mathematical Biology

The Journal of Mathematical Biology (JOMB) utilizes diverse mathematical disciplines to advance biological understanding. It publishes papers providing new insights through rigorous mathematical analysis or innovative mathematical tools, with a focus on accessibility to biologists.

• Covers cell biology, genetics, ecology, and more
• Welcomes survey and perspective papers
• Encourages proposals for topical collections
• All submissions undergo single-blind peer review
• Final decisions are made by Editors-in-Chief
• Thomas Hillen,
• Anna Marciniak-Czochra

Societies and partnerships

Latest articles

A two-phase thin-film model for cell-induced gel contraction incorporating osmotic effects.

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Infection-induced increases to population size during cycles in a discrete-time epidemic model

• Laura F. Strube
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The role of memory-based movements in the formation of animal home ranges

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Phylogenetic network classes through the lens of expanding covers

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Memory effects in disease modelling through kernel estimates with oscillatory time history

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Journal updates

The karl-peter hadeler prize winner 2023.

The ESMTB Award Committee unanimously recommend the article titled "Pulled, pushed or failed: the demographic impact of a gene drive can change the nature of its spatial spread" by Lena Kläy, Léo Girardin, Vincent Calvez and Florence Débarre for the Karl-Peter Hadeler prize 2023.

The authors make an important contribution to the analysis of pushed and pulled waves in systems of partial differential equations (PDEs) for genetic drive/wild type invasions. They make new connections between genetic invasions and PDE modelling that allows them to gain relevant ecological insights into observations that result from genetic diversity. The paper is particularly well suited for the K.P. Hadeler prize as K.P. Hadeler himself has published on pulled and pushed invasion waves.

Read and share the article freely using the following link:  https://rdcu.be/dzSn7

The Karl-Peter Hadeler Prize Winner 2022

The ESMTB Award Committee unanimously recommend the article titled "Spatial ecology, optimal control and game theoretical fishing problems" by Idriss Mazari and Domènec Ruiz-Balet for the Karl-Peter Hadeler prize 2022. The mathematical results presented in this article are interesting and well-integrated with the underlying ecological problem, of which they genuinely support a more in-depth theoretical understanding. Both authors are young researchers at an early stage of their academic careers and will thus certainly benefit from being awarded the KPH prize.

Read and share the article freely using the following link:  https://rdcu.be/c5Z46

The Karl-Peter Hadeler Prize

The Karl-Peter Hadeler Prize of the Journal of Mathematical Biology (JoMB) recognizes outstanding publications in the journal.

Call for Papers: Topical Collection on Epidemic Modelling in Honour of Fred Brauer

Fred Brauer, one of the pioneers in mathematical epidemiology, passed away on October 17, 2021, leaving a legacy of exceptional contributions to the field of epidemic modelling including his independent and collaborative research, and his mentorship of multiple generations of researchers in the field.

We are pleased to edit a topical collection for the Journal of Mathematical Biology in his honour. The topical collection covers all areas of epidemiological modelling defined broadly but focuses on using mathematical approaches to gain epidemiological understanding or explain epidemiological phenomena. 

Submission Deadline: 31 October 2022 (Extended)

Guest Editors:  Jianhong Wu, York University; Carlos Castillo-Chavez, Arizona State University; Zhilan Julie Feng, Purdue University; Christopher Kribs, University of Texas at Arlington; Shigui Ruan, University of Miami.

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Korunes, KL; Myers, RB; Hardy, R; Noor, MAF

Drosophila pseudoobscura is a classic model system for the study of evolutionary genetics and genomics. Given this long-standing interest, many genome sequences have accumulated for D. pseudoobscura and closely related species D. persimilis, D. miranda, and D. lowei. To facilitate the exploration… read more about this publication  »

Zipple, MN; Roberts, EK; Alberts, SC; Beehner, JC

Bartoš et al. (2021; Mammal Review 51: 143–153; https://doi.org/10.1111/mam.12219) reviewed the mechanisms involved in the ‘Bruce effect’ – a phenomenon originally documented in inseminated female house mice Mus musculus, who block pregnancy following exposure to a novel (non-sire) male. They argue… read more about this publication  »

Byrne, M; Koop, D; Strbenac, D; Cisternas, P; Yang, JYH; Davidson, PL; Wray, G

The molecular mechanisms underlying development of the pentameral body of adult echinoderms are poorly understood but are important to solve with respect to evolution of a unique body plan that contrasts with the bilateral body plan of other deuterostomes. As Nodal and BMP2/4 signalling is involved… read more about this publication  »

Wang, Q; Xu, P; Sanchez, S; Duran, P; Andreazza, F; Isaacs, R; Dong, K

BackgroundInsects rely on their sense of smell to locate food and hosts, find mates and select sites for laying eggs. Use of volatile compounds, such as essential oils (EOs), to repel insect pests and disrupt their olfaction-driven behaviors has great practical significance in integrated pest… read more about this publication  »

Castano-Duque, L; Ghosal, S; Quilloy, FA; Mitchell-Olds, T; Dixit, S

Rice production is shifting from transplanting seedlings to direct sowing of seeds. Following heavy rains, directly sown seeds may need to germinate under anaerobic environments, but most rice (Oryza sativa) genotypes cannot survive these conditions. To identify the genetic architecture of complex… read more about this publication  »

Peng, L; Shan, X; Wang, Y; Martin, F; Vilgalys, R; Yuan, Z

Clitopilus hobsonii (Entolomataceae, Agaricales, Basidiomycetes) is a common soil saprotroph. There is also evidence that C. hobsonii can act as a root endophyte benefitting tree growth. Here, we report the genome assembly of C. hobsonii QYL-10, isolated from ectomycorrhizal root tips of Quercus… read more about this publication  »

Yan, W; Wang, B; Chan, E; Mitchell-Olds, T

The genetic basis of flowering time changes across environments, and pleiotropy may limit adaptive evolution of populations in response to local conditions. However, little information is known about how genetic architecture changes among environments. We used genome-wide association studies (GWAS… read more about this publication  »

Doak, DF; Waddle, E; Langendorf, RE; Louthan, AM; Isabelle Chardon, N; Dibner, RR; Keinath, DA; Lombardi, E; Steenbock, C; Shriver, RK; Linares, C; Begoña Garcia, M; Funk, WC; Fitzpatrick, SW; Morris, WF; Peterson, ML

Structured demographic models are among the most common and useful tools in population biology. However, the introduction of integral projection models (IPMs) has caused a profound shift in the way many demographic models are conceptualized. Some researchers have argued that IPMs, by explicitly… read more about this publication  »

Kim, JH; Hilleary, R; Seroka, A; He, SY

A grand challenge facing plant scientists today is to find innovative solutions to increase global crop production in the context of an increasingly warming climate. A major roadblock to global food sufficiency is persistent loss of crops to plant diseases and insect infestations. The United… read more about this publication  »

Yuan, M; Jiang, Z; Bi, G; Nomura, K; Liu, M; Wang, Y; Cai, B; Zhou, J-M; He, SY; Xin, X-F

The plant immune system is fundamental for plant survival in natural ecosystems and for productivity in crop fields. Substantial evidence supports the prevailing notion that plants possess a two-tiered innate immune system, called pattern-triggered immunity (PTI) and effector-triggered immunity (… read more about this publication  »

Benito-Kwiecinski, S; Giandomenico, SL; Sutcliffe, M; Riis, ES; Freire-Pritchett, P; Kelava, I; Wunderlich, S; Martin, U; Wray, GA; McDole, K; Lancaster, MA

The human brain has undergone rapid expansion since humans diverged from other great apes, but the mechanism of this human-specific enlargement is still unknown. Here, we use cerebral organoids derived from human, gorilla, and chimpanzee cells to study developmental mechanisms driving evolutionary… read more about this publication  »

Lofgren, LA; Nguyen, NH; Vilgalys, R; Ruytinx, J; Liao, H-L; Branco, S; Kuo, A; LaButti, K; Lipzen, A; Andreopoulos, W; Pangilinan, J; Riley, R; Hundley, H; Na, H; Barry, K; Grigoriev, IV; Stajich, JE; Kennedy, PG

While there has been significant progress characterizing the 'symbiotic toolkit' of ectomycorrhizal (ECM) fungi, how host specificity may be encoded into ECM fungal genomes remains poorly understood. We conducted a comparative genomic analysis of ECM fungal host specialists and generalists,… read more about this publication  »

Mitchell, RM; Ames, GM; Wright, JP

Background and aimsUnderstanding impacts of altered disturbance regimes on community structure and function is a key goal for community ecology. Functional traits link species composition to ecosystem functioning. Changes in the distribution of functional traits at community scales in response to… read more about this publication  »

DeMarche, ML; Bailes, G; Hendricks, LB; Pfeifer-Meister, L; Reed, PB; Bridgham, SD; Johnson, BR; Shriver, R; Waddle, E; Wroton, H; Doak, DF; Roy, BA; Morris, WF

Spatial gradients in population growth, such as across latitudinal or elevational gradients, are often assumed to primarily be driven by variation in climate, and are frequently used to infer species' responses to climate change. Here, we use a novel demographic, mixed-model approach to dissect the… read more about this publication  »

Shaw, EC; Fowler, R; Ohadi, S; Bayly, MJ; Barrett, RA; Tibbits, J; Strand, A; Willis, CG; Donohue, K; Robeck, P; Cousens, RD

Aim: If we are able to determine the geographic origin of an invasion, as well as its known area of introduction, we can better appreciate the innate environmental tolerance of a species and the strength of selection for adaptation that colonizing populations have undergone. It also enables us to… read more about this publication  »

Rushworth, CA; Mitchell-Olds, T

Despite decades of research, the evolution of sex remains an enigma in evolutionary biology. Typically, research addresses the costs of sex and asexuality to characterize the circumstances favoring one reproductive mode. Surprisingly few studies address the influence of common traits that are, in… read more about this publication  »

Jorge, JF; Bergbreiter, S; Patek, SN

Small organisms can produce powerful, sub-millisecond impacts by moving tiny structures at high accelerations. We developed and validated a pendulum device to measure the impact energetics of microgram-sized trap-jaw ant mandibles accelerated against targets at 105 m s-2 Trap-jaw ants (… read more about this publication  »

Markunas, AM; Manivannan, PKR; Ezekian, JE; Agarwal, A; Eisner, W; Alsina, K; Allen, HD; Wray, GA; Kim, JJ; Wehrens, XHT; Landstrom, AP

Long QT syndrome (LQTS) is a genetic disease resulting in a prolonged QT interval on a resting electrocardiogram, predisposing affected individuals to polymorphic ventricular tachycardia and sudden death. Although a number of genes have been implicated in this disease, nearly one in four… read more about this publication  »

Stone, DF; Mccune, B; Pardo-De La Hoz, CJ; Magain, N; Miadlikowska, J

The new genus Sinuicella, an early successional lichen, was found on bare soil in Oregon, USA. The thallus is minute fruticose, grey to nearly black, branching isotomic dichotomous, branches round, 20-90 μm wide in water mount. The cortex is composed of interlocking cells shaped like jigsaw puzzle… read more about this publication  »

Oita, S; Ibáñez, A; Lutzoni, F; Miadlikowska, J; Geml, J; Lewis, LA; Hom, EFY; Carbone, I; U'Ren, JM; Arnold, AE

Understanding how species-rich communities persist is a foundational question in ecology. In tropical forests, tree diversity is structured by edaphic factors, climate, and biotic interactions, with seasonality playing an essential role at landscape scales: wetter and less seasonal forests… read more about this publication  »

Hibshman, JD; Webster, AK; Baugh, LR

Standard laboratory culture of Caenorhabditis elegans utilizes solid growth media with a bacterial food source. However, this culture method limits control of food availability and worm population density, factors that impact many life-history traits. Here, we describe liquid-culture protocols for… read more about this publication  »

Caves, EM; Green, PA; Zipple, MN; Bharath, D; Peters, S; Johnsen, S; Nowicki, S

AbstractSensory systems are predicted to be adapted to the perception of important stimuli, such as signals used in communication. Prior work has shown that female zebra finches perceive the carotenoid-based orange-red coloration of male beaks-a mate choice signal-categorically. Specifically,… read more about this publication  »

Reed, PB; Peterson, ML; Pfeifer-Meister, LE; Morris, WF; Doak, DF; Roy, BA; Johnson, BR; Bailes, GT; Nelson, AA; Bridgham, SD

Predicting species' range shifts under future climate is a central goal of conservation ecology. Studying populations within and beyond multiple species' current ranges can help identify whether demographic responses to climate change exhibit directionality, indicative of range shifts, and whether… read more about this publication  »

Sallee, JL; Crawford, JM; Singh, V; Kiehart, DP

Actin filament crosslinking, bundling and molecular motor proteins are necessary for the assembly of epithelial projections such as microvilli, stereocilia, hairs, and bristles. Mutations in such proteins cause defects in the shape, structure, and function of these actin - based protrusions. One… read more about this publication  »

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REPORTS, ARTICLES AND RESEARCH PAPERS

Endangered species.

    • Paving the Road to Extinction: Congress’ Expanded Assault on Endangered Species Through Appropriations Poison-Pill Riders .Kurose, S., and Hartl, B., Center for Biological Diversity, January 2024.     • Recovery of the Grizzly Bear at the Intersection of Law and Science . Greenwald, N. August 2023.     • No Refuge: How America’s National Wildlife Refuges Are Needlessly Sprayed With Nearly Half a Million Pounds of Pesticides Each Year . Connor, H. May 2018.     • Mexico's 10 Most Iconic Endangered Species . Olivera, A. April 2018.      • A Wall in the Wild: The Disastrous Impacts of Trump's Border Wall on Wildlife . Greenwald, N., Segee, B., Curry, T. and Bradley, C. May 2017.      • Pollinators in Peril: A Systematic Status Review of North American and Hawaiian Native Bees . Kopec, K., Center for biological Diversity, February 2017.      • Removing the Walls to Recovery: Top 10 Species Priorities for a New Administration. Endangered Species Coalition (including the Center). December 2016.      • Shortchanged: Funding Needed to Save America's Most Endangered Species . Greenwald, N., Hartl, , B., Mehrhoff, L., Pang, J. December 2016.      • Taxa, Petitioning Agency, and Lawsuits Affect Time Spent Awaiting Listing Under the US Endangered Species Act . Greenwald, N., Kesler, D., Puckett, E. Biological Conservation . September 2016.      • Fishing Down Nutrients on Coral Reefs . Allgeier, J.E., Valdivia,A., Cox, C. & Layman, C.A. Nature Communications . August 2016.      • A Wild Success: A Systematic Review of Bird Recovery Under the Endangered Species Act . Suckling, K., Mehrhoff, L., 2016. Beam, R. & Hartl, B. June 2016.      • Poisoned Waters: How Cyanide Fishing and the Aquarium Trade Are Devastating Coral Reefs and Tropical Fish . Center for Biological Diversity & For the Fishes. June 2016.     • Lethal Loophole: How the Obama Administration Is Increasingly Allowing Special Interests to Endanger Rare Wildlife . Sanerib, T., Elkins, C., and Greenwald, N. February 2016.     • Biodiversity on the Brink: The Role of “Assisted Migration" in Managing Endangered Species Threatened With Rising Seas . Lopez, J. Harvard Environmental Law Review Vol. 39. 2015.     • Politics of Extinction: The Unprecedented Republican Attack on Endangered Species and the Endangered Species Act . Pand, J., and Greenwald, N. July 2015.     • Runaway Risks: Oil Trains and the Government's Failure to Protect People, Wildlife and the Environments . Margolis, J., 2015.     • Sea-Level Rise and Species Survival along the Florida Coast . Lopez, J. 2014.     • Collision Course: The Government's Failing System for Protecting Florida Manatees from Deadly Boat Strikes . Center for Biological Diversity. September 2014.      • Nourished by Wildfire: The Ecological Benefits of the Rim Fire and the Threat of Salvage Logging . Center for Biological Diversity and John Muir Projejct, January 2014.      • Deadly Waters: How Rising Seas Threaten 233 Endangered Species . Center for Biological Diversity. 2013.     • In Harm's Way: How the U.S. State Department and U.S. Fish and Wildlife Service Have Ignored the Dangers of the Keystone XL Pipeline to Endangered Species . Burd, L., Greenwald, N., & Bradley, C., 2013.     • Dying for Protection: The 10 Most Vulnerable, Least Protected Amphibians and Reptiles in the United States . Adkins Giese, C. 2013.     • On Thin Ice: After Five Years on the Endangered Species List, Polar Bears Still Face a Troubling Future . Center for Biological Diversity. 2013.     • A Poor Track Record, but a Chance to Excel . Snape, W., 2013. The Environmental FORUM   Environmental Law Institute, www.eli.org ) 30(1): 53.     • Can A Multi-Species Habitat Conservation Plan Save San Diego's Vulnerable Vernal Pool Species? Buse, J., 2012. Golden Gate University Environmental Law Journal 6(1): 52-80.     • On Time, On Target: How the Endangered Species Act Is Saving America's Wildlife . Suckling, K., Greenwald, N., Curry, T. 2012.     • Protecting Rare Amphibians Under the U.S. Endangered Species Act . Adkins Giese, C., FrogLog (May 2012): 21-23.     • White-nose Syndrome Headed to a Cave Near You . Matteson, M. Desert Report (June 2011): 6-7.     • Impact of Dunes Sagebrush Lizard on Oil and Gas Activities in New Mexico . Lininger, J. & Bradley, C., 2011.    • Assessing Protection for Imperiled Species of Nevada, U.S.A.: Are Species Slipping Through the Cracks of Existing Protections? Bradley, C. & Greenwald, N., 2008.     • Not Too Late to Save the Polar Bear: A Rapid Action Plan to Address the Arctic Meltdown . Siegel, K., Cummings, B., Moritz, A. & Nowicki, B., 2007.     • Status of the Bald Eagle in the Lower 48 States and the District of Columbia: 1963-2007 . Suckling, K. & Hodges, W., 2007.     • The Bureaucratically Imperiled Mexican Wolf . Povilitis, A., Parsons, D.R., Robinson, M.J., & Becker, C.D., 2006.     • A Review of Northern Goshawk Habitat Selection in the Home Range and Implications for Forest Management in the Western United States . Greenwald, D. N., Crocker-Bedford, C., Broberg, l., & Suckling, K., 2005.     • Suitable Habitat for Jaguars in New Mexico . Robinson, M., Bradley, C., Boyd, J., 2005.     • Impacts of the 2003 Southern California Wildfires on Four Species Listed as Threatened or Endangered Under the Federal Endangered Species Act: Quino Checkerspot Butterfly, Mountain Yellow-legged Frog, Coastal California Gnatcatcher, Least Bell's Vireo . Bond, M. & Bradley, C., 2003.     • A Conservation Alternative for the Management of the Four Southern California National Forests (Los Padres, Angeles, San Bernardino, Cleveland) . Penrod, K., et al., 2002.     • Analysis of Compliance by U.S. Forest Service Southwestern Region with Incidental Take Statements Issued by the U.S. Fish and Wildlife Service in Three Biological Opinions of 1999 . Taylor, M. 2001.

ENDANGERED SPECIES ACT

   • Taxa, Petitioning Agency, and Lawsuits Affect Time Spent Awaiting Listing Under the US Endangered Species Act . Greenwald, N., Kesler, D., Puckett, E. Biological Conservation . September 2016.     • A Wild Success: A Systematic Review of Bird Recovery Under the Endangered Species Act . Suckling, K., Mehrhoff, L., Beam, R. & Hartl, B. June 2016.     • Saving Species and Wild Spaces: 10 Extraordinary Places Saved by the Endangered Species Act , Pang, J. & Hartl, B. May 2016.     • Politics of Extinction: The Unprecedented Republican Attack on Endangered Species and the Endangered Species Act . Pang, J., and Greenwald, N. July 2015.     • A Different Perspective on the Endangered Species Act at 40 Responding to Damien M. Schiff . Buse, J., 2015. University of California, Davis 38(1): 145-166.     • Making Room for Wolf Recovery: The Case for Maintaining Endangered Species Act Protections for America's Wolves . Weiss, A., Greenwald, N. & Bradey, C. Center for Biological Diversity, November 2014.     • A Wild Success: American Voices on the Endangered Species Act at 40 . Center for Biological Diversity, Endangered Species Coalition, Defenders of Wildlife, February 2014.     • On Time, On Target: How the Endangered Species Act Is Saving America's Wildlife . Suckling, K., Greenwald, N., Curry, T., 2012.     • A Future for All: A Blueprint for Strengthening the Endangered Species Act . 2011.     • Effects on Species' Conservation of Reinterpreting the Phrase “Significant Portion of its Range” in the U.S. Endangered Species Act . Greenwald, N., 2009. Conservation Biology 23(6): 1375-1377.     • State Endangered Species Acts . In Baur, D.C. & Irvin, W.R. (eds.), Endangered Species Act: Law, Policy, and Perspectives , second edition. American Bar Association. George, S. & Snape, W., 2010.     • Politicizing Extinction: The Bush Administration's Dangerous Approach to Endangered Wildlife . Greenwald, N., 2007.     • Measuring the Success of the Endangered Species Act, Recovery Trends in the Northeastern United States . Suckling, K.F., 2006.     • Factors Affecting the Rate and Taxonomy of Species Listings under the US Endangered Species Act . In Gobel, D, Scott, M.J. & Davis, F.W. (eds.), The Endangered Species Act at Thirty: Renewing the Conservation Commitment . Island Press. Greenwald, D.N., Suckling, K.F. & Taylor, M.F.J., 2006.     • Critical Habitat and Recovery . In: Gobel, D., Scott, M.J. & Davis, F.W. (eds.), The Endangered Species Act at Thirty: Renewing the Conservation Commitmen t. Island Press. Suckling, K.F. & Taylor, M.F.J., 2006.     • The Listing Record . In Gobel, D., Scott, M.J., & Davis, F.W. (eds.), The Endangered Species Act at Thirty: Renewing the Conservation Commitmen t. Island Press. Greenwald, D.N., K.F. Suckling and M.F.J. Taylor, 2006.      • Progress or Extinction? A Systematic Review of the U.S. Fish and Wildlife Service's Endangered Species Act Listing Program. 1974-2004 . Greenwald, D. N. & Suckling, K. F., 2005     • The Effectiveness of the Endangered Species Act: A Quantitative Analysis . Taylor, M.F.J., Suckling, K.F. & Rachlinski, J.J., 2005. BioScience 55(4): 360-367.     • Extinction and the Endangered Species Act . Suckling, K., Nowicki, B. & Slack, R., 2004.     • A Review of the Bush Critical Habitat Record . 2003.     • Bush Administration Attacks Endangered Species Act .     • Safeguarding Citizen Rights Under the Endangered Species Act . Senatore, M., & Suckling, K., 2001.

BIODIVERSITY

    • Hidden In Plain Sight: California's Native Habitats Are Valuable Carbon Sinks . Yap, T., Prabhala, A., Anderson, I. Center for Biological Diversity. July 2023.     • Bullfrogs: A Trojan Horse for a Deadly Fungus? Yap, T., Koo, M., Ambrose, R., Vredenburg, V.T. Science Journal for Kids . October 2018.     • Mexico's 10 Most Iconic Endangered Species . Olivera, A. April 2018.     • A Multi-method Approach to Delineate and Validate Migratory Corridors . Bond, M., Bradley, C., Kiffner, C., Morrison, T., and Lee, D. Landscape Ecology . May 2017.    • Biodiversity on the Brink: The Role of “Assisted Migration" in Managing Endangered Species Threatened With Rising Seas . Lopez, J. Harvard Environmental Law Review Vol. 39. 2015.    • Nourished by Wildfire: The Ecological Benefits of the Rim Fire and the Threat of Salvage Logging . Center for Biological Diversity and John Muir Projejct, January 2014.    • Joining the Convention on Biological Diversity: A Legal and Scientific Overview of Why the United States Must Wake Up . Snape, B., 2010. Sustainable Development Law & Policy 10(3): 6-18.    • Highways to Hell: A Critical Examination of the Environmental Impacts of the Security and Prosperity Partnership . Lopez, J., 2009. [3 MB version]    • Rana Aurora (Northern Red-legged Frog) Egg Mass Disturbance. Curry, T. R., and Hayes, M. P., 2009. Herpetological Review 40(2): 208-209.    • Greenwashing Risks to Baby-boomers Abroad: An Assessment of Available Strategies to Address “Green” Marketing Misrepresentation to U.S. Retiree Real Estate Investors Overseas. 2009.    • Life History Diversity and Protection of the Southwestern Washington/Columbia River Distinct Population Segment of the Coastal Cutthroat Trout . Greenwald, N. & Mashuda, S., 2008.     • Predation on the Coastal Tailed Frog ( Ascaphus truei ) by a Shrew ( Sorex spp.) in Washington State . Lund, E., Hayes, M., Curry, T., Marsten, J. & Young, 2008. Northwestern Naturalist 89(3): 200-202.     • Assessing Protection for Imperiled Species of Nevada, U.S.A.: Are Species Slipping Through the Cracks of Existing Protections? Greenwald, N. & Bradley, C., 2008.     • Medicinal Plants at Risk — Nature's Pharmacy, Our Treasure Chest: Why We Must Preserve Our Natural Heritage . Roberson, E., 2008.     • Species of Concern of the Tillamook Rainforest and North Coast, Oregon . Greenwald, N. & Garty, A., 2007.     • The Bering Sea: A Biodiversity Assessment of Vertebrate Species . Greenwald, N., Callimanis, S., Garty, A. & Peters, E., 2006.     • Saving All the Parts: Protecting Species of Northwest Old-growth Forests . Greenwald, N. & Greason, S., 2004.     • Imperiled Western Trout and the Importance of Roadless Areas . 2001.     • A Conservation Alternative for the Management of the Four Southern California National Forests (Los Padres, Angeles, San Bernardino, Cleveland) . Penrod, K., et al., 2002.     • Principles of Wildlife Corridor Design . Bond, M., 2003.

    • A  Wall  of  Lights  Through the Wild: 1,800 Stadium Lights on Arizona Conservation Lands Threaten Wildlife . McSpadden, R., Jordahl, L., and Bradley, C. Center for Biological Diversity. June 2023.     • Hidden In Plain Sight: California's Native Habitats Are Valuable Carbon Sinks . Yap, T., Prabhala, A., Anderson, I. Center for Biological Diversity. July 2023.     • Deadpool Highway: How Interstate 11 Would Worsen Arizona’s Water Crisis . McSpadden, R., and Bradley, C. Center for Biological Diversity. May 2023.     • State of Utom River 2022: Challenges, Opportunities for Southern California’s Signature River . Center for Biological Diversity. August 2022.     • A Wall in the Wild: The Disastrous Impacts of Trump's Border Wall on Wildlife . Greenwald, N., Segee, B., Curry, T. and Bradley, C. May 2017.     • A Multi-Method Approach to Delineate and Validate Migratory Corridors . Bond, M., Bradley, C., Kiffner, C., Morrison, T., and Lee, D. Landscape Ecology . May 2017.     • Public Lands Enemies: 15 Federal Lawmakers Plotting to Seize, Destroy and Privatize America's Public Lands . Spivak, R. & Beam, R. March 2017.     • Runaway Risks: Oil Trains and the Government's Failure to Protect People, Wildlife and the Environments . Margolis, J., 2015.     • Nourished by Wildfire: The Ecological Benefits of the Rim Fire and the Threat of Salvage Logging . Center for Biological Diversity and John Muir Projejct, January 2014.     • Groups Join Together to Confront Water-rights Issue . Mrowka, R. Desert Report (June 2011): 2, 13.     • Saving Our National Legacy: The Future of America's Last Heritage Forests . Fink, M., Kassar, C., Matteson, M., and McKinnon, T., July 2009.     • America's Newest Fossil Beds National Monument: Tule Springs/Upper Las Vegas Wash . Mrowka, R. and Davis, L., 2009.     • Wild at Heart: Saving the Last of America's Backcountry . 2008.     • Imperiled Western Trout and the Importance of Roadless Areas . 2001.     • Protection and Conservation of Roadless Areas in the Southwest . Greenwald, N.     • A Conservation Alternative for the Management of the Four Southern California National Forests (Los Padres, Angeles, San Bernardino, Cleveland) . Penrod, K., et al., 2002.

CLIMATE CHANGE

   • Flight Path: A Trajectory for U.S. Aviation to Meet Global Climate Goals . Center for Biological Diversity. October 2020.    • From Bailout to Righting the Course: The Commonsense Action the United States Must Take to Address the Flood Crisis . Lopez, J. 2020.    • Stealing California's Future: How Monterey County's Dirty Oil Business Worsens the Climate Crisis . Center for Biological Diversity. September 2016.    • Throwing Shade: 10 Sunny States Blocking Distributed Solar Development . Greer, R. April 2016.    • Up in the Air: How Airplane Carbon Pollution Jeopardizes Global Climate Goals . Pardee, V. December 2015.    • Biodiversity on the Brink: The Role of “Assisted Migration" in Managing Endangered Species Threatened With Rising Seas . Lopez, J. Harvard Environmental Law Review Vol. 39. 2015.    • Grounded: The President's Power to Fight Climate Change, Protect Public Lands by Keeping Publicly Owned Fossil Fuels in the Ground . Saul, M., McKinnon, T., Spivak, R., 2015.    • What Happens When Species Move But Reserves Do Not? Creating Climate Adaptive Solutions to Climate Change . Whipps, N., 2015. Hastings Law Journal Vol. 66.    • Runaway Risks: Oil Trains and the Government's Failure to Protect People, Wildlife and the Environments . Margolis, J., 2015.    • The Potential Greenhouse Gas Emissions From U.S. Federal Fossil Fuels . Ecoshift Consulting, Center for Biological Diversity, Friends of the Earth. August 2015.    • Troubled Waters: Offshore Fracking's Threat to California's Ocean, Air and Seismic Stability . Center for Biological Diversity, 2014.    • On Shaky Ground: Fracking, Acidizing, and Increased Earthquake Risk in California . Earthworks, Center for Biological Diversity, Clean Water Action, 2014.    • Deadly Waters: How Rising Seas Threaten 233 Endangered Species . Center for Biological Diversity, 2013.    • The New Normal: Climate Change Victims in Post- Kiobel United States Federal Courts . Lopez, J., 2013. Charleston Law Review 8(1).    • Not Just a Number: Achieving a CO 2 Concentration of 350 ppm or Less to Avoid Catastrophic Climate Impacts. Center for Biological Diversity and 350.org, 2010.    • Extinction: It's Not Just for Polar Bears. A Center for Biological Diversity and Care for the Wild International report. Wolf, S., 2010.    • Yes, He Can: President Obama's Power to Make an International Climate Commitment Without Waiting for Congress . Bundy, K., Cummings, B., Pardee, V. & Siegel, K., 2009.    • 350 Reasons We Need to Get to 350: Species Threatened by Global Warming; An Interactive Installation by the Center for Biological Diversity . 2009.    • No Reason to Wait: Reducing Greenhouse Gas Emissions Through the Clean Air Act . Siegel, K., Snape, W., and Vespa, M., June 2009.    • Why 350? Climate Policy Must Aim to Stabilize Greenhouse Gases at the Level Necessary to Minimize the Risk of Catastrophic Outcomes . Vespa, M., 2009. Ecology Law Currents 36(1): 185-194. • Fuel to Burn: The Climate and Public Health Implications of Off-road Vehicle Pollution in California . Kassar, C. & Spitler, P., 2008.     • Not Too Late to Save the Polar Bear: A Rapid Action Plan to Address the Arctic Meltdown . Siegel, K., Cummings, B., Moritz, A. & Nowicki, B., 2007.     • The California Environmental Quality Act: On the Front Lines of California's Fight Against Global Warming . Siegel, K., Vespa, M. & Nowicki, B., 2007.

    • Powerless in the United States: How Utilities Drive Shutoffs and Energy Injustice . Center for Biological Diversity, March 2023.     • Rooftop-Solar Justice: Why Net Metering is Good for People and the Planet and Why Monopoly Utilities Want to Kill It . Crystal,. H., Lin, R., and Su, J., Center for Biological Diversity, Energy and Policy Institute, BailoutWatch, January 2023.    • Fueling Extinction: How Dirty Energy Drives Wildlife to the Brink . Endangered Species Coalition (incl. the Center for Biological Diversity), 2012.    • A Deadly Toll: The Gulf Oil Spill and the Unfolding Wildlife Disaster . 2011. Center for Biological Diversity.    • What We Should Learn From the BP Spill . Lopez, J., 2011. Environmental Law News 20 (1): 35.    • Too Much Oil for the Rubber Stamp: The Government's Role in the BP Oil Spill . Lopez, J., 2011.    • BP's Well Evaded Environmental Review: Categorical Exclusion Policy Remains Unchanged . Lopez, J., 2010. Ecology Law Currents 37 (93): 93-103.    • Corporate Profile of Salt River Project . Draffan, G., 2001.    • Ecological and Community Problems with Biomass-to-Energy . Schulke, T.

ENVIRONMENTAL HEALTH/POLLUTION

    • Collateral Damage: How Factory Farming Drives Upthe Use of Toxic Agricultural Pesticides . Center for Biological Diversity, World Animal Protection, 2022.     • Pesticides and Environmental Injustice in the USA: Root Causes, Current Regulatory Reinforcement and a Path Forward . Donley, N., Bullard, R., Economos, J., Figueroa, I., Lee, J., Liebman, A., Navarro Martinez, D., & Shafiei, F. BMC Public Health , April 2022.     • Toxic Hangover: How the EPA Is Approving New Products With Dangerous Pesticides It Committed to Phasing Out . Donley, N., Jan. 2020.     • A Menace to Monarchs: Drift-prone Dicamba Poses a Dangerous New Threat to Monarch Butterflies . Donley, N., March 2018.     • Toxic Concoctions: How the EPA Ignores the Dangers of Pesticide Cocktails . Donley, N., July 2016.     • Can't We Just All Get Along: Reconciling Pesticide Use and Species Protection . Lopez, J. 2015.     • Lost in the Mist: How Glyphosate Use Disproportionately Threatens California's Most Impoverished Counties . Center for Biological Diversity, 2015.       • Perdido en la niebla: Como El uso de glifosato desproporcionadamente amenaza los condados más pobres de California . Center for Biological Diversity, 2015.     • Dispersants: The Lesser of Two Evils or a Cure Worse Than the Disease? Kilduff, C. and Lopez, J., 2012. Ocean and Coastal Law Journal 16 (2): 375-394.     • Endocrine-disrupting Chemical Pollution: Why the EPA Should Regulate These Chemicals Under the Clean Water Act . Lopez, J., 2010. Sustainable Development Law & Policy 10(3): 19-23.     • Poisoning Our Imperiled Wildlife: San Francisco Bay Area Endangered Species at Risk from Pesticides . Miller, J., Miller, J., Beeland, T.D. & Bradley, C., 2006.     • Silent Spring Revisited: Pesticide Use and Endangered Species . Litmans, B. & Miller, J, 2004.

POPULATION AND SUSTAINABILITY

    • Alternative Economies: Uplifting Activities for a Sustainable Future . Dennings, K., Adoma, A.; 2023.     • At What Cost: Unraveling the Harms of the Fast Fashion Industry . Shedlock, K., Feldstein, S.; 2023.     • Too Hot for Knitwear: Climate Crisis, Biodiversity and Fashion Brands Using Woll and Synthetics . Feldstein, S., Hakansson, E.; 2023.     • Talking Trash: U.S. Perspectives on the Language of Waste Reduction . Dennings, K., Adoma, A.; 2023.     • Unwrapped: Perceptions of Winter Holiday Consumerism, Gift Giving and Waste . Dennings, K., Adoma, A; 2023.     • The Influence of Environmental Toxicity, Inequity and Capitalism on Reproductive Health . Dennings, K., Grossman, A; 2022.     • Gender and the Climate Crisis: Equitable Solutions for Climate Plans . Dennings, K., Baillie, S., and Baxter, C; 2022.     • Public Perceptions on Population: US Survey Results . Dennings, K., Baillie, S., Ricciardi, R. and Addo, A; 2022; Population and Sustainability 6(1): 1-23.     • Sheer Destruction: Wool, Fashion and the Biodiversity Crisis . Feldstein, S., Hakansson, E., Katcher, J., Vance, V.; 2021.     • Endangered Species Condoms: A Social Marketing Tool for Starting Conversations About Population . Baillie, S., Dennings, K. and Feldstein S.; 2020; Journal of Population and Sustainability 4(2): 31-44.     • Contraception and Consumption in the Age of Extinction: U.S. Survey Results . Dennings, K., 2020.     • Appetite for Change: A Policy Guide to Reducing Greenhouse Gas Emissions of U.S. Diets by 2030 . Feldstein, S., 2020.     • Catering to the Climate: How Earth-Friendly Menus at Events Can Help Save the Planet . Molidor, J., Emery., I., 2019.     • Towards a Psychology of the Food‐Energy‐Water Nexus: Costs and Opportunities . Dreyer, S.J., Kurz, T., Prosser, A.M.B., Abrash, A.W., Dennings, K., McNeill, I., Saber, D.A., Swim, J.K., 2019. Journal of Social Issues 76(1).     • Slow Road to Zero: A Report Card on U.S. Supermarkets’ Path to Zero Food Waste . Molidor, J., Feldstein, S., Figueiredo, J., 2019.     • Checked Out: How U.S. Supermarkets Fail to Make the Grade in Reducing Food Waste . Molidor, J., Feldstein, S., 2018.     • Wasting Biodiversity: Why Food Waste Needs to Be a Conservation Priority . Feldstein, S., 2017. Biodiversity 18 (2-3): 75-77.     • Habitat-Fed Food: Grass-fed Beef and Sustainable Solutions . Molidor, J., 2017. Biodiversity 18 (2-3): 78-81.

FIRE AND FOREST RESTORATION

    • Nourished by Wildfire: The Ecological Benefits of the Rim Fire and the Threat of Salvage Logging . Center for Biological Diversity and John Muir Projejct, January 2014.     • Influence of Pre-Fire Tree Mortality on Fire Severity in Conifer Forests of the San Bernardino Mountains, California , 2009. Bond, M., Lee, D. E., Bradley, C. & Hanson, T. Open Forest Science Journal 2:41-47.     • Impacts of the 2003 Southern California Wildfires on Four Species Listed as Threatened or Endangered Under the Federal Endangered Species Act: Quino Checkerspot Butterfly, Mountain Yellow-legged Frog, Coastal California Gnatcatcher, Least Bell's Vireo . Bond, M. & Bradley, C., 2003.     • Ecological Restoration of Southwestern Ponderosa Pine Ecosystems: A Broad Perspective . Allen, C.D., Savage, M., Falk, D.A., Suckling, K. F., Swetnam, T. W., Schulke, T., Stacey, P. B., Morgan, P., Hoffman, M. & Klingel, J. T., 2002. Ecological Applications 12(5): 1418-1433.     • Prelude to Catastrophe: Recent and Historic Land Management within the Rodeo-Chedeski Fire Area .     • Effectively Treating the Wildland-Urban Interface to Protect Houses and Communities from the Threat of Forest Fire . Nowicki, B., 2002.     • Protection and Conservation of Roadless Areas in the Southwest . Greenwald, N.     • An Ecologically Integrated Approach to Managing Dwarf Mistletoe (Arceuthobium) in Southwest Forests .  Pollock, Michael M., Ph. D.  Kieran Suckling, 1995.      • A Conservation Alternative for the Management of the Four Southern California National Forests (Los Padres, Angeles, San Bernardino, Cleveland) . Penrod, K., et al., 2002.     • Fire & Forest Ecosystem Health in the American Southwest . Suckling, K., 1996.

LIVESTOCK GRAZING

    • Costs and Consequences: The Real Price of Livestock Grazing on America's Public Lands . Glaser, C., Romaniello, C. & Moskowitz, K. (prepared for the Center for Biological Diversity), 2015.     • Assessing the Full Cost of the Federal Grazing Program . Moskowitz, K., & Romaniello, C., 2002.     • Ecological Restoration of Southwestern Ponderosa Pine Ecosystems: A Broad Perspective . Allen, C.D., Savage, M., Falk, D.A., Suckling, K.F., Swetnam, T.W., Schulke, T., Stacey, P.B., Morgan, P., Hoffman, M. & Klingel, J.T., 2002. Ecological Applications 12(5): 1418-1433.     • Cattle Grazing and the Loss of Biodiversity in the East Bay .      • Livestock Grazing, Fire Regimes, and Tree Densities: A Literature Review .

    • Frogs . In Bernheimer, K. (ed.), Brothers and Beasts: An Anthology of Men on Fairy Tales. Wayne State University Press. Suckling, K.F., 2007.     • Biodiversity, Linguistic Diversity and Identity — Toward an Ecology of Language in an Age of Extinction . Suckling, K., 2000. Langscape 17: 14-20.     • A House on Fire: Connecting the Biological and Linguistic Diversity Crises . 2002. Animal Law 6: 193-202.

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Biological Warfare: Infectious Disease and Bioterrorism

The term biological warfare typically conjures images of medieval warriors tossing dead cattle over city walls or clandestine government agents secretly releasing mysterious microbes into enemy territory. Of course, biological warfare does encompass such activity, but the vast majority of what constitutes biological warfare is far more mundane. Ever since life evolved on earth about 3.8 billion years ago, organisms have constantly devised new ways to kill each other. Any organism that makes use of toxins—from bacteria to snakes—is engaging in a form of biological warfare. Humans who engage in biological warfare do so by taking advantage of these toxin-producing organisms.

Introduction

The term biological warfare typically conjures images of medieval warriors tossing dead cattle over city walls or clandestine government agents secretly releasing mysterious microbes into enemy territory. Of course, biological warfare does encompass such activity, but the vast majority of what constitutes biological warfare is far more mundane. Ever since life evolved on Earth about 3.8 billion years ago, organisms have constantly devised new ways to kill each other. Any organism that makes use of toxins—from bacteria to snakes—is engaging in a form of biological warfare. Humans who engage in biological warfare do so by taking advantage of these toxin-producing organisms.

The Natural History of Biological Warfare

An entire textbook could be filled with examples of organisms that employ toxins to kill other organisms. We therefore touch only briefly on the natural history of biological warfare.

Bacteria are particularly adept at biological warfare. While humanity finds antibiotics incredibly useful in our battle against infectious disease, bacteria did not create them for our benefit. Instead, they make antibiotics to kill off other bacteria that are competing for the same habitat or resources. Similarly, bacteria synthesize toxic proteins known as bacteriocins to kill their relatives because closely related strains of bacteria are likelier to compete with each other. For example, many strains of Escherichia coli deploy a wide variety of bacteriocins (referred to as colicins) intended to kill other strains of E. coli . The genes for colicins are normally carried on plasmids, and many of these plasmids are commonly used in molecular biology and genetic engineering (see Chapter 3). Yersinia pestis, the plague bacterium, also makes bacteriocins (called pesticins in this case) designed to kill competing strains of its own species ( Fig. 22.1 ).

Bacteriocins Inhibit Other Bacteria

A bacteriocin-producing strain of Lactococcus in a piece of cheese can inhibit the growth of a related microorganism.

A point of clarification: The distinction between bacteriocin and toxin has to do with the target. Bacteria deploy bacteriocins against their fellow—often closely related—bacteria with the deliberate intention of killing them. In contrast, proteins produced by bacteria that act against higher organisms are referred to as toxins . Perhaps counterintuitively, pathogenic bacteria do not usually “intend” to kill the organisms they infect. Rather, they want to manipulate them long enough to survive and reproduce. The longer the host stays alive, the longer it provides a home for the infecting bacteria. Just like antibiotics, some bacterial toxins are useful to humans. The bacterium Bacillus thuringiensis produces an insect-killing toxin that is harmless to vertebrates, and this “Bt toxin” has been used extensively in genetically modified crops. (See Chapter 15.)

Lower eukaryotes also regularly engage in biological warfare. Paramecium , a ciliated protozoan, carries symbiotic bacteria (Caedibacter) known as kappa particles that grow and divide inside the larger eukaryotic cell ( Fig. 22.2 ).

Killer Paramecium Uses a Bacterial Toxin

(A) The kappa particles are found in the cytoplasm of the Paramecium. (B) Kappa particles are symbiotic Caedibacter that are found in many strains of Paramecium, yet they have their own DNA and divide like typical bacteria.

Strains of Paramecium with kappa particles are known as killers and, due to unknown genetic factors and resistance mechanisms, are naturally tolerant of them. Killer strains release kappa particles into the environment, and if a sensitive Paramecium (i.e., one lacking the ability to harbor kappa particles) eats and digests just a single kappa particle, a protein toxin is released and kills the Paramecium. Interestingly, the toxin is not encoded by a gene on the bacterial chromosome, but on a plasmid derived from a defective bacteriophage. So a toxin encoded by a virus infecting the kappa particle bacterium has been commandeered for the purpose of killing other strains of Paramecium.

This phenomenon is not at all unusual. Many toxins used by pathogenic bacteria that infect humans are actually encoded by foreign DNA of nonchromosomal origin, such as viruses, plasmids, or transposons. These elements are often integrated into the chromosome of pathogenic strains of bacteria. For example, the only strains of Corynebacterium diphtheriae —the causative agent of diphtheria—that are dangerous to humans are the ones that carry a toxin-encoding virus.

Higher eukaryotes can either create their own toxins—such as the venom produced by snakes and scorpions—or expropriate toxins produced by other species. One species of caterpillar that feeds on tobacco plants can exhale noxious nicotine at spiders, chasing them away. Other insects rely on microbes to wage biological warfare. Certain parasitic wasps inject their eggs into the maggots (i.e., larvae) of plant-eating insects. After the eggs hatch, the newborn wasps eat the living maggots from the inside ( Fig. 22.3 ).

Wasps Use Viruses against Maggots

Certain types of wasps lay their eggs inside tobacco hornworm larvae. The wasp lands on the back of the larva and injects the eggs plus adenovirus into the maggot through the ovipositor. The adenovirus prevents the larva from eating and therefore developing into a pupa. When the eggs hatch, the young use the insides of the larva as a food source, to grow and develop into adult wasps.

The maggots are eventually killed, and a new generation of wasps is released. The secret to the wasp’s success is the injection of an adenovirus along with the eggs. The virus targets the maggot’s “fat body” (vaguely equivalent to the liver of higher animals) and cripples the maggot’s developmental control system and immune system. The maggot loses its appetite for plants and is prevented from molting and turning into a pupa, the next stage in its life cycle.

Many different kinds of organisms engage in biological warfare. Bacteria kill other bacteria with antibiotics or bacteriocins. They also make toxins that are targeted at higher organisms. Eukaryotes can either make their own toxins or commandeer those produced by lower organisms.

Microbes Versus Man: The Rise of Antibiotic Resistance

Although we rarely perceive it this way, infectious disease is just another manifestation of biological warfare that is ubiquitous throughout life. The evolutionary relationship between hosts and pathogens is essentially a never-ending arms race. When a pathogen evolves a new toxin, the host evolves a response to it. Humanity has taken this arms race one step further by utilizing technology such as vaccines and industrial-scale manufacturing of antibiotics. However, the microbes are fighting back.

Perhaps the biggest problem plaguing medical microbiology today is the rise of antibiotic resistance. There are many reasons why bacteria have developed this resistance, but all of the explanations have one thing in common: the proliferation and misuse of antibiotics. For instance, medical doctors often prescribe antibiotics to patients who have an infection, even if it is unknown whether the disease is bacterial. Other times, the wrong antibiotic is prescribed. In many developing countries, antibiotics can be bought over the counter without a prescription. Compounding the dilemma, patients who receive antibiotics often do not comply with the recommended dose, ending treatment as soon as they feel better. This has the effect of selecting for the survival of the bacteria that have already developed a slight resistance to the drug. When the patient propagates the infection, he unintentionally passes on these toughened survivors. The widespread use of antibiotics in animal feed—which farmers use to fatten up livestock—is also a major contributor to the problem.

Today, many experts worry about “incurable” infections. Methicillin-resistant Staphylococcus aureus (MRSA) gets a lot of media attention, but it is not the only worrisome microbe. There have been reports from around the world of totally drug-resistant tuberculosis, which as the name implies, appears to be resistant to all treatment. In a 2013 report, the Centers for Disease Control and Prevention (CDC) issued an urgent warning about infections from (1) Clostridium difficile , which causes diarrhea and is often acquired by patients in health-care settings who were treated with antibiotics for other infections; (2) Carbapenem-resistant Enterobacteriaceae (CRE), such as Klebsiella and E. coli , which also cause health-care-associated infections and may be resistant to all known antibiotics; and (3) Neisseria gonorrhoeae , the etiologic agent of gonorrhea, which is growing in resistance to several antibiotics.

While these developments are alarming, much research is being done to combat the rise of antibiotic resistance. Although microbes have responded to our antibiotic assault, we are developing some new weapons to regain the upper hand.

Novel Targets for Antibiotics

Although there has been speculation of an inevitable “post-antibiotic era,” there are still plenty of opportunities for the development of novel antibiotics.

One strategy is to attack previously unexploited vulnerable spots in a bacterium’s metabolism or life cycle, preferably those that bacteria cannot easily defend by acquiring resistance. For instance, bacteria use iron chelators, known as siderophores , to bind iron and extract it from host proteins. Siderophores are excreted, bind iron, and are then taken back into bacteria by specialized transport systems. Absence of high-potency siderophores largely abolishes virulence in both plague and tuberculosis. Because mammals do not make siderophores, their unique biosynthetic pathways provide an attractive target for development of novel antibiotics. Yersiniabactin, the siderophore of several pathogenic Yersinia species, is capped by a salicyl group ( Fig. 22.4 ).

Salicyl-AMS Inhibits the Production of Yersiniabactin

The structure of yersiniabactin shows the salicyl group in red. The precursor, salicyl-AMP, is made by activating salicylate with ATP. The sulfamoyl analog, salicyl-AMS, inhibits the incorporation of the salicyl group into yersiniabactin.

The intermediate in the pathway, produced when ATP activates salicylate, is salicyl-AMP. A chemically synthesized analog of salicyl-AMP, called salicyl-AMS, replaces the phosphate with a sulfamoyl group. The compound is highly active and specifically inhibits siderophore synthesis. This prevents the growth of Yersinia under iron-limiting conditions, such as encountered in the human body.

Another strategy is to screen novel microbes for antibiotics. As discussed earlier, bacteria produce antibiotics for the explicit purpose of killing other bacteria. Since most microbes that exist in nature have neither been cultured nor identified, it is likely that many natural antibiotics have yet to be discovered. In 2013, a new antibiotic, called anthracimycin, was isolated from an Actinomycete that lives in the ocean. The new antibiotic is active against Bacillus anthracis and MRSA, and modifying it with chlorine groups expanded its spectrum of activity.

Yet another strategy is to identify and clone potential antimicrobial biosynthetic pathways. For example, based on its DNA sequence, one research group cloned a biosynthetic gene cluster from an Actinomycete called Saccharomonospora that was predicted to produce an antimicrobial lipopeptide. Expressing the gene cluster resulted in the discovery of a new antibiotic, taromycin A. The major advantage of this technique is that it can be applied to microbes that are difficult to culture in the laboratory.

A different approach is to disrupt existing antibiotic resistance, rather than developing new antibiotics. For example bacteriophage, such as those that live in the human gut, can shuttle antibiotic resistance genes between bacteria. Consequently, developing drugs that kill or disable bacteriophage is an innovative way to combat the spread of antibiotic resistance. Additionally, disrupting bacterial quorum sensing has been suggested. Bacteria use quorum sensing as a communication system in order to coordinate behavior ( Fig. 22.5 ).

Quorum Sensing

Bacteria can coordinate behavior by detecting the presence of a signal molecule that indicates the density of the population.

By releasing particular chemical compounds into the environment, bacteria can detect when a threshold population density, or “quorum,” has been reached. Many pathogens construct antibiotic-resistant biofilms after the population has reached a particular density. Disrupting their communication system would cripple their ability to coordinate behavior and keep the bacteria more vulnerable to antibiotics.

Phage Therapy and Bacterial Predators

The history of phage therapy —that is, using bacteriophage (also called “phage”) to treat bacterial infections—begins in France in 1921. That year, microbiologist Felix d’Hérelle used phage to treat patients suffering from dysentery ( Fig. 22.6 ).

Felix d’Hérelle

Microbiologist Felix d’Hérelle helped pioneer phage therapy.

In 1927, he also used phage therapy to treat cholera victims in south Asia. Unfortunately, many other scientists in the United States and elsewhere were unable to replicate his work, and when the widespread production of antibiotics started in 1945, the scientific community mostly lost interest in phage therapy. The French, however, enthusiastically practiced phage therapy into the 1990s and, during those seven decades, there were reports of successful treatment of typhoid fever, colitis, septicemia, skin infections, and various other bacterial diseases. Other countries that embraced phage therapy include Poland, Russia, and Georgia. Today, patients there can receive phage therapy for chronic and antibiotic-resistant bacterial infections.

Since the 1990s, the Western scientific community has renewed its interest in phage therapy. One benefit of using phage, as opposed to antibiotics, is their specificity. Antibiotics kill many different types of bacteria—which is harmful if they destroy helpful gut bacteria—but individual phage species infect only a group of very closely related bacteria. Every bacterial infection could, in theory, be targeted by a highly specific phage.

As predicted, however, bacteria also can develop resistance to phage, mainly through thwarting viral attachment. Now, researchers are investigating the use of lysins , a class of toxins that phage use to dismantle bacterial cell walls as part of their lytic cycle ( Fig. 22.7 ). Because lysins target conserved regions within peptidoglycan, it is believed that bacteria will be less able to develop resistance. Lysins work best against Gram-positive bacteria, but genetic engineering can expand the spectrum of activity to include Gram-negative bacteria also.

Bacteriophage Tsamsa Kills Bacillus anthracis

The lysin isolated from the bacteriophage Tsamsa kills Bacillus anthracis and other closely related species.

As an alternative to phage, it may be possible to deploy predatory bacteria against human pathogens. Bdellovibrio , which invades other bacteria rather like a virus, and Micavibrio , which attaches to bacterial cell surfaces, have been shown to kill antibiotic-resistant pathogenic bacteria in vitro .

Fighting Pathogens with Genetic Engineering

Because of a persistent fear that we will run out of novel antibiotics, many clever new technologies have been suggested to fight bacterial infections. Some of the most promising of these antibiotics utilize genetic engineering.

For example, many pathogenic Escherichia coli use the FimH adhesin to bind to mammalian cells via mannose residues on surface glycoproteins. Several alkyl- and aryl-mannose derivatives bind with extremely high affinity to the adhesin and block its attachment to the natural receptor. Such mannose derivatives, therefore, could serve as anti-adhesin drugs. However, manufacturing pharmaceuticals is quite expensive. It would be far cheaper to genetically engineer nonpathogenic strains of E. coli to express the mannose derivatives on their cell surfaces. Pathogenic bacteria would then bind to these decoys instead of to mammalian cells. This would also avoid the need for continuous administration of sugar derivatives because the decoy strains of E. coli would multiply naturally in the intestine. Alternatively, nonpathogenic strains of E. coli could be engineered with genes for adhesins that would allow them to compete with pathogens for mammalian cell receptors. (Such engineered strains would also have the advantage of being able to deliver protein pharmaceuticals or large segments of DNA for gene therapy into mammalian cells.)

A different approach is to generate altered toxins that interfere with their natural analogs. Typical A-B bacterial toxins are made from a single “active” A subunit, which carries out a toxic enzymatic reaction inside a target cell, and often several “binding” B subunits, which serve as a delivery system by attaching to the cell surface. Because several properly functioning binding subunits are required to deliver the active subunit, one approach to antitoxin therapy relies on utilizing dominant-negative mutations in the binding subunit of the toxin. The mechanism involves the binding of a defective protein subunit to functional subunits resulting in a complex that is inactive overall. (The term dominant-negative refers to mutations in which an abnormal gene product sabotages the activity of the wild-type gene product. Consequently, most dominant-negative mutations affect proteins with multiple subunits.) Dominant-negative mutations have been deliberately isolated in the B protein (called the “protective antigen”) of anthrax toxin. Mixing mutant subunits with wild-type ones resulted in the assembly of inactive heptamers that bind the A subunits (called “lethal factor” and “edema factor”) of anthrax toxin. As a result, the toxic A subunits cannot be transported into target cells ( Fig. 22.8 ). This technique has been shown to protect both cultured human cells and whole mice or rats from death by lethal levels of anthrax toxin.

Dominant-Negative Mutations

For anthrax, the B subunit (called PA63 protein or “protective antigen”) binds the A subunits (called lethal factor, LF, and edema factor, EF) and transports them into the target cell cytoplasm via an endocytic vesicle. The dominant-negative inhibitory (DNI) mutant of the PA63 protein (purple) assembles together with normal PA63 monomers (pink) to give an inactive complex that cannot release the LF and EF toxins from the vesicle into the cytoplasm.

Fighting Pathogens with Nanotechnology

Many of the advances in nanotechnology aimed at fighting pathogens involve the creation of bactericidal surfaces (see Chapter 7 for more on nanotechnology). Several metals are inherently antibacterial. For instance, silver ions kill bacteria through several mechanisms, such as generating reactive oxygen species and disrupting protein disulfide bonds. Surfaces coated with silver, selenium, and copper nanoparticles all show antimicrobial activity.

Metals are not the only option. A substance known as “black silicon” is made of tiny “nanopillars” that are able to physically destroy bacteria, including endospores, through mechanical stress ( Fig. 22.9 ). Antimicrobial activity has also been demonstrated with stacked carbon nanotubes called nanocarpets (see Chapter 7). Additionally, polymers of esters and cyclic hydrocarbons reduce attachment of bacteria. Such discoveries could allow for improved sanitation in health-care settings and the manufacture of antimicrobial medical devices.

Antibiotic resistance is a growing concern, but contrary to popular reports, it is not necessarily an intractable problem. Novel targets for antibiotics, phage therapy, genetic engineering, and nanotechnology provide multiple possibilities for fighting antibiotic-resistant pathogens.

Nanostructures Can Kill Bacteria

Scanning electron micrograph of black silicon surface showing its hierarchical structures. (A) Periodically arranged micropillar arrays; (B) a micropillar with nanostructures; (C) nanostructures formed on the top of the micropillar.

A Brief History of Human Biological Warfare

Throughout history, humans have devised new and innovative ways to kill other humans. When technology was primitive, warriors used whatever nature provided. Burning crops was probably the easiest and earliest form of warfare aimed at undermining an enemy, as was poisoning a community’s drinking water with dead or rotting animals.

Early Human Biological Warfare

Slightly more advanced forms of biological warfare emerged when soldiers began dipping spears in feces and throwing poisonous snakes. During the Black Death epidemic of the mid-1300s, the Tartars catapulted plague-ridden corpses over the walls into cities held by their European enemies. Although this is sometimes credited with spreading the plague, rats and their fleas were far more effective at spreading bubonic plague than contact with corpses ( Fig. 22.10 ).

Bubonic Plague

This painting by Arnold Böcklin, simply titled Plague , depicts the fear that bubonic plague provoked in antiquity.

Given the state of hygiene in most medieval towns or castles, there was little need to provide an outside source of infection. With plague, typhoid, smallpox, dysentery, and diphtheria already around, all that was usually necessary was to let nature take its course. Similarly, a widespread myth exists that European settlers purposefully infected Native Americans with smallpox. While it is true that the British military attempted this strategy during the French and Indian War in the mid-1700s, the vast majority of Native American deaths—perhaps as much as 95% of the population—were due to inadvertent infection with smallpox and other diseases.

The truth is, until very recently, humans were not particularly hygienic. Consider, for instance, that antiseptic surgery—invented by Joseph Lister and now considered a mainstay of modern medicine—wasn’t widely adopted until the late 1870s. Before then, armies and civilian populations were so dirty and disease-ridden that practicing germ warfare was like throwing mud on a pig. It is only in our modern hygienic age that biological warfare has become a more meaningful threat.

Modern Human Biological Warfare and Bioterrorism

Modern biological warfare began during World War I. Although the Germans refused to use biological agents against people, they did use them against animals, infecting Allied horses with glanders ( Burkholderia mallei ) and anthrax. The French also employed glanders against German horses. During World War II, the infamous Japanese Unit 731 experimentally infected Chinese prisoners of war with horrifying diseases, such as cholera, epidemic hemorrhagic fever, and venereal disease. It was also responsible for dropping plague-infected “flea bombs” on cities in China, although this likely had little effect partly because plague was already endemic to the region ( Fig. 22.11 ).

Japanese military Unit 731 killed thousands of Chinese people with experimental infections and biological warfare.

After World War II, particularly during the Korean War, the United States ratcheted up its biological weapons program. Perhaps the most controversial aspect of the program was the purposeful release of biological agents, such as the relatively harmless Serratia marcescens , over American cities to study weapons dispersal. The military unintentionally infected 11 civilians, one of whom died. By 1969, the U.S. had weaponized anthrax and tularemia. However, in 1975, the U.S. renounced all biological weapons by signing the Biological Weapons Convention (BWC).

The Soviet Union also signed the BWC but then deceitfully enlarged its efforts. The scope of the Soviet program was astonishing. The Soviets manufactured several hundred tons of anthrax, and an accidental release in 1979 killed 66 people. The former USSR also made thousands of pounds of smallpox and plague, and in 1989, they supposedly managed to weaponize Marburg virus, which causes a deadly hemorrhagic fever similar to Ebola. These allegations remain unconfirmed. Finally, under President Boris Yeltsin in 1992, Russia ended its biological weapons program, but the fate of the weapons stockpiles remains unclear.

Today, biological warfare is feared less from nations and more from terrorist groups or “lone wolves.” But there is disagreement over just how much of a threat this poses. Many believe that terrorists would be incapable of carrying out an effective, large-scale biological attack. For instance, in 1984, the Rajneesh cult gave food poisoning to about 750 citizens of a small Oregon town for political purposes by adding Salmonella to salad bars. Aum Shinrikyo, a Japanese cult that perpetrated a sarin gas attack in the Tokyo subway in 1995, experimented with biological weapons, but to no avail. The 2001 U.S. anthrax attack (discussed in more detail in the following section) killed only 5 people. Skeptics point to incidents like these as evidence that bioterrorists are incapable of inflicting widespread damage. Other analysts disagree ( Fig. 22.12 ).

Bioterrorism

Some experts believe that a large-scale bioterrorist attack will occur in the not-too-distant future, but others say bioterrorism is an ineffective tactic. Attack methods include contamination of food and water supplies (A), bombs (B), using the mail (C), contamination of water (F), spraying aerosolized agents (E, G), direct injection (D), or the infiltration of “suicide infectees” (H).

Some biological agents, such as anthrax, require little expertise to grow or weaponize. With microbiological information universally available on the Internet, some experts believe that it is just a matter of time before a large bioterrorist attack occurs. A small crop duster airplane loaded with anthrax and flown over a major city could potentially kill hundreds of thousands if not millions of people. Exacerbating the problem is the fact that a 2010 federal commission found the United States to be completely unprepared in the event of a bioterrorist attack.

Psychological Impact and Cost

During the Vietnam War, the Viet-Cong guerillas dug camouflaged pits as booby traps. Inside, they often positioned sharpened bamboo stakes or splinters smeared with human waste. Although it was possible to contract a nasty infection from these, the main purpose was psychological. The tactic worked. The response of American troops was to alter their movements in a way that was disproportionate to the actual threat. An analogous scenario played out following the 2001 anthrax attack in the United States in which there was a colossal disruption of postal services and massive new expenses. Yet, only 5 people died in the attack. (Compare that to the roughly 62,000 Americans who died from influenza and pneumonia that same year.)

Both of these examples serve to underscore two important points: First, biological warfare will almost certainly have a far greater psychological impact than direct impact; and second, protective measures against biological attacks are costly and inconvenient. For instance, giving soldiers vaccines against all possible biological agents would be impractical and possibly dangerous if they have been developed under emergency conditions without thorough testing. Also, vaccines have side effects. Consider the anthrax vaccine used by the U.S. army that was approved in 1971. Vaccination requires six inoculations plus annual boosters. It produces swelling and irritation at the site of injection in 5% to 8% and severe local reactions in about 1% of those inoculated, although major systemic reactions are rare. Although it works against “natural” exposure, it is uncertain whether it would protect against a concentrated aerosol of anthrax spores.

Or consider the smallpox vaccine ( Fig. 22.13 ). For every 1 million people vaccinated, the CDC estimates that 1,000 people will have serious side effects, 14 to 52 people will have life-threatening side effects, and 1 or 2 people will die. Is it worth vaccinating an entire army or nation—knowing ahead of time that many will die or become sick—to protect them against an unlikely threat? From an epidemiological standpoint, the answer is clearly no, which explains why citizens do not receive smallpox vaccinations. The general rule in public health is to vaccinate only if the risk of the disease is greater than the risk of vaccination.

Smallpox Vaccine

How the normal skin reaction to smallpox vaccination progresses in two patients.

Even if widespread vaccination is forgone in favor of other measures, such as protective clothing or respirators, there is still the financial cost. A nation that invests heavily in bioterrorism preparedness could have spent that money in more productive ways. Dressing troops in special clothing and equipment could promote heat stress or make them easier targets for conventional weaponry. Additionally, medications taken prophylactically to prevent infectious diseases are expensive, rarely 100% effective, and may have long-term negative health consequences.

Biological warfare has been practised since ancient times. However, it has only rarely been effective. Naturally occurring infectious diseases have killed far more people. Still, bioterrorism may pose a serious threat today. Even if an attack kills relatively few people, the psychological impact could be enormous.

Identifying Suitable Biological Warfare Agents

Biological warfare is used to kill, injure, and psychologically intimidate enemies. Many naturally occurring diseases are effective agents, although it might be possible to “improve” them with genetic engineering, as discussed later.

What makes for an effective biological agent? Five major factors need to be considered.

Preparation. Some pathogenic microorganisms are relatively easy to grow in culture, whereas others are extremely difficult or expensive to manufacture in sizeable quantities. Viruses, for instance, can grow only inside host cells, and culturing animal cells is more complex than growing bacteria. Similarly, pathogenic eukaryotes such as Plasmodium (malaria) or Entamoeba (amoebic dysentery) are difficult to culture on a large scale, although some pathogenic fungi can be grown relatively easily. Bacteria are generally the easiest to manufacture on a large scale, but most bacterial infections can be cured with antibiotics. Viruses, though more difficult to grow, have the advantage of being largely incurable despite a small and growing range of specific antiviral agents.

Another factor is weaponization . The disease agent must be prepared in a manner that facilitates storage and dispersal. Because bacterial cells and spores tend to clump together spontaneously, they must be weaponized to allow effective delivery.

Dispersal. Dispersal is a particular challenge for biological weapons. The most likely option would be some form of airborne delivery. However, if applied outdoors, this tactic would be vulnerable to the whims of the weather. Not only is a pleasant breeze required, but also the wind needs to blow in the right direction! During the 1950s, the British government conducted field tests with harmless bacteria. When the wind blew them over farmland, many of the airborne bacteria survived the trip and reached the ground alive. In contrast, when the wind blew the bacteria over industrial areas, especially oil refineries or similar installations, the airborne bacteria were almost all killed. Ironically, air pollution may help protect an urban population from a bioterrorist attack. To aerosolize a biological agent for an indoor attack, a building’s ventilation system or a medical nebulizer could be used ( Fig. 22.14 ).

A medical nebulizer could be used to aerosolize a biological agent for an indoor attack. Two general types of nebulizer are in use: the jet nebulizer that uses pressurized gas and the ultrasonic nebulizer that relies on ultrasonic vibrations.

Persistence. Persistence may be the most difficult factor to consider. On the one hand, the biological agent should be able to persist in storage until it is ready to be deployed, and it must survive long enough in the environment to infect the enemy. On the other hand, it should not persist so long that the victor is unable to invade and conquer enemy territory.

Many infectious agents are sensitive to desiccation and become inactive if exposed to air for significant periods of time. Moreover, natural UV radiation from the sun also inactivates many bacteria and viruses. Thus, most biological warfare agents must be protected from this “open air factor” before use and then dispersed as rapidly as possible. For instance, many viruses last only a few days, if even that, outside their animal or human hosts. (However, infections due to these agents may persist among the local population.)

Anthrax is often chosen as a biological weapon because of its ability to persist for long periods of time. The bacterium Bacillus anthracis, which causes the disease, spreads by forming spores that are tough and difficult to destroy ( Fig. 22.15 ). When suitable conditions return, for example, inside the lungs of a human, the spores germinate and resume growth as normal bacterial cells, releasing life-threatening toxins.

Spores of Bacillus anthracis

Anthrax spores, which are seen here forming inside bacterial cells, are difficult to destroy and last a very long time.

Incubation time. A problem unique to biological warfare, compared to conventional weapons, is that death or incapacitation from infectious disease is a relatively slow process. Even the most virulent pathogens, such as Ebola virus or pneumonic plague, can take a few days to kill. An infected enemy would therefore still be capable of fighting for a significant period. Yet, a biological agent that kills too quickly may not have time to spread among the enemy population.

High-containment laboratories. High-containment laboratories are needed for research and development of infectious biological agents. Biological containment is rated on a scale with four levels. Biosafety level 1 (BSL-1) microbes are mostly harmless, such as nonpathogenic E. coli . BSL-2 organisms are human pathogens, but not easily transmitted in the laboratory, such as Salmonella . BSL-3 organisms are dangerous and often can be transmitted via aerosol, such as tuberculosis and SARS. BSL-4 laboratories are for extremely dangerous and easily transmissible microbes, such as Ebola.

The whole BSL-4 laboratory is sealed off and kept at a little under normal atmospheric pressure. In case of a leak, outside air will flow into the laboratory, helping ensure contaminated air will remain there instead of seeping out. Operations are conducted inside safety cabinets with glove ports. To enter a BSL-4 lab, a researcher must use an air lock and exchange outside clothes for a separate set of lab clothes, including a special “spacesuit” that is equipped with its own air supply ( Fig. 22.16 ).

Biohazard Clothing, Then and Now

(A) Even during the bubonic plague, doctors wore protective clothing to prevent exposure to the deadly pathogens. The large beak was often stuffed with flowers and herbs to create a pleasant scent that was thought to keep away the plague, as illustrated in Bartholin, Thomas Hafniae, 1654–1661: Historiarum anatomicarum.

Courtesy U.S. National Library of Medicine.

(B) Today’s suits are more scientific and streamlined, but serve the same purpose. Laboratory worker wearing BSL-4 protective gear.

When finished, a scientist leaves behind his lab clothes and uses an exit equipped with disinfectant showers and ultraviolet lights. Some high-containment labs are designed so that the only exit is via total submersion in a pool of disinfectant. Ultraviolet lights are used to sterilize both the laboratories themselves and the air locks, especially when working with viruses.

Using high-containment facilities for research is expensive and time consuming. For manufacturing biological weapons on an industrial scale, the inconveniences are correspondingly worse. However, terrorist groups or rogue nations may only care about secrecy and may be willing to forgo biosafety considerations. The U.S. Army’s criteria for a biowarfare agent are given in Box 22.1 .

Five major factors that influence the use of a biological warfare agent include preparation, dispersal, persistence, incubation time, and the necessity of high-containment laboratories. A variety of viruses, bacteria, and toxins have been proposed as effective agents. These are classified into three categories by the Centers for Disease Control and Prevention (CDC) according to their level of risk.

Requirements for Biological Warfare Agents

According to the U.S. Army, a biological warfare agent should fulfill the following requirements:

• 1. It should consistently produce death, disability, or damage.
• 2. It should be capable of being produced economically and in militarily adequate quantities from available materials.
• 3. It should be stable under production and storage conditions, in munitions, and in transportation.
• 4. It should be capable of being disseminated efficiently by existing techniques, equipment, or munitions.
• 5. It should be stable after dissemination from a military munition.

A Closer Look at Select Biological Warfare Agents

The Centers for Disease Control and Prevention (CDC) has classified biological warfare agents into three categories based on the potential level of threat they pose to society. These categories are summarized in Table 22.1 . Anthrax was used in the 2001 bioterror attack in the USA (see Box 22.2 ).

CDC-Listed Agents Relevant to Biological Warfare

The 2001 Anthrax Attack in the United States

Shortly after the terrorist attack on the World Trade Center in September 2001, anthrax spores were distributed via the U.S. Postal Service. The anthrax attack was notable in two respects. First, it killed only a small handful of victims, supporting the contention that biological warfare is not usually very effective in practice. Second, it generated a vastly disproportionate reaction, illustrating the importance of the psychological aspects of bioterrorism. Undoubtedly, governmental overreaction and public panic did far more damage than the anthrax attack itself.

An insider in America’s own biodefense research establishment perpetrated the attack. Detectives believe the culprit was Bruce Ivins, an army scientist and anthrax expert, but he committed suicide in 2008 without ever being charged. The FBI officially closed the case in 2010. However, doubts surrounding the evidence against Ivins have led some observers to call for a new investigation.

The attacker used the Ames strain of Bacillus anthracis, which is widely used in laboratories across the United States. A major problem with tracing the origin of anthrax outbreaks is that all the various strains of Bacillus anthracis are closely related and difficult to tell apart. No differences in either 16S rRNA or 23S rRNA sequence occur between different strains. In practice, analysis is done using single-nucleotide polymorphisms (SNPs) or variable number tandem repeats (VNTRs; see Chapter 23). For example, the vrrA gene of Bacillus anthracis contains from two to six copies of the sequence CAATATCAACAA within the coding region for a protein of unknown function ( Fig. A ).

The vrrA VNTR of Bacillus anthracis

The vrrA gene of anthrax (blue) has a stretch of repeats in the coding region. Different strains of anthrax have different numbers of repeats (green) due to polymerase slippage and can therefore be traced by comparing the number of repeats. PCR is used to amplify the region containing the repeats. The length of the PCR product reveals the number of repeats.

These repeats were probably originally generated by slippage of DNA polymerase during replication. The repeats do not alter the reading frame, but result in corresponding repeats of the four-amino-acid sequence Gln-Tyr-Gln-Gln within the encoded protein. Several other VNTRs are also now used, including some on the pOX1 virulence plasmid. The greatest diversity of Bacillus anthracis strains, as assessed by multiple VNTR analysis, comes from southern Africa, which is therefore regarded as the probable homeland of anthrax.

Anthrax and Other Bacterial Agents

Anthrax is a virulent disease of cattle that infects humans quite easily. It is caused by the bacterium Bacillus anthracis, which is relatively easy to culture and forms spores, which can survive harsh conditions that would kill most bacteria. The spores may lie dormant in the soil for years and then germinate on contact with a suitable animal victim.

Three main forms of anthrax occur. Cutaneous anthrax, that is, infection of the skin, is rarely dangerous. Gastrointestinal anthrax occurs mostly in grazing animals and is relatively rare among humans, although it can occur via ingestion of bacteria or spores from contaminated meat. Inhalational anthrax, in which the spores enter via the lungs, gives a high death rate. In many ways, anthrax is the ideal biological weapon—lethal, highly infectious, and cheap to produce, with spores that store well.

The problem with anthrax, however, is that the spores are so tough and long-lived that getting rid of them after hostilities are over is nearly impossible. During World War II, the British tested anthrax (using sheep as the targets) on the tiny island of Gruinard, which lies off the coast of Scotland. Although it was firebombed and disinfected, the island remained uninhabitable for nearly 50 years because of anthrax spores still surviving in the soil. Finally, in 1990, the island was declared safe after it was treated with a solution of formaldehyde and seawater. The indestructibility of anthrax spores would thus be problematic for a military occupation, but it could be useful as a defense mechanism. Anthrax spores seeded into the soil of sparsely populated land could serve to protect against foreign invaders.

Yersinia pestis, the causative agent of bubonic plague, was responsible for the notorious Black Death epidemics of the Middle Ages and is a current bioterrorism threat. Plague is typically spread by flea bites. However, aerosolized bacteria can cause the pneumonic form of plague. This form of the disease is highly infectious and has a mortality rate close to 100% if untreated. Besides Japan’s use of plague as a biological weapon during World War II (discussed previously), the British biological warfare center at Porton Down maintained large-scale plague cultures for several years following the war. In the 1960s, the United States experimented with spreading plague among rodents in Vietnam, Laos, and Cambodia to little practical effect. Because it can be obtained relatively easily from nature, plague may be an attractive weapon for bioterrorists ( Fig. 22.17 ).

Plague Reservoir

Rodents, such as squirrels and prairie dogs, serve as a natural reservoir for plague. A California ground squirrel is shown here.

An unconfirmed report in 2009 indicated that 40 al-Qaeda terrorists in Algeria accidentally became infected with plague and died, presumably from a biological weapons experiment gone awry.

Other potential bacterial agents include the following:

• ■ Brucella. Brucellosis is a disease of cattle, camels, goats, and related animals. Brucellosis was developed as a biological weapon by the United States from 1954 to 1969. In humans, it behaves erratically, both in the time for symptoms to emerge and the course of the disease. Although human victims often fall severely ill for several weeks, it is rarely fatal, even if untreated. It could be used as an incapacitating agent.
• ■ Francisella tularensis. Tularemia is a disease of rodents or birds that has a death rate of 5% to 10% in humans if untreated. It is highly infectious and generally regarded as an incapacitating agent.
• ■ Burkholderia pseudomallei. Melioidosis is related to glanders (Burkholderia mallei), a disease of horses. Melioidosis is a rare disease of rodents from the Far East that is spread by rat fleas. Melioidosis is more virulent than glanders and, untreated, is fatal some 95% of the time in humans.

In many ways, anthrax is one of the best biological weapons. It is lethal, highly infectious, and easy to produce, and it has long-lasting spores. Plague is also lethal, and its pneumonic form can spread from person to person. Potential incapacitating agents include brucellosis and tularemia.

Smallpox and Other Viral Agents

Variola , the viral etiologic agent of smallpox , is a member of the poxvirus family. These large viruses contain double-stranded (ds) DNA ( Fig. 22.18 ).

Variola Virus

Poxviruses, including smallpox, are closely related in structure and DNA sequence. They have genomes of dsDNA surrounded by two envelope layers. A protein layer, known as the palisade, is embedded within the core envelope. Premade viral enzymes are also packaged with the genome to allow replication immediately on infection. Poxviruses infect animals, and the outermost viral membrane is derived from the membrane of the previous host cell.

Poxviruses are the most complex animal viruses and are so large they may be seen with a light microscope. They measure approximately 0.4 by 0.2 microns, compared to 1.0 by 0.5 microns for bacteria such as E. coli. Unlike other animal DNA viruses, which replicate inside the cell nucleus, poxviruses replicate their dsDNA in the cytoplasm of the host cell. They build subcellular factories known as inclusion bodies, inside which virus particles are manufactured. Poxviruses have 185,000 nucleotides encoding 150 to 200 genes, about the same number as the T4 family of complex bacterial viruses.

Variola virus infects only humans, which allowed its eradication by the World Health Organization, a task completed by 1980. Smallpox is highly infectious and exists as two variants: Variola major with a fatality rate of 30% to 40% and Variola minor with a fatality rate of around 1% ( Fig. 22.19 ). Their genome sequences differ by approximately 2%. Vaccinia virus is a related, mild poxvirus of unknown origin that is used as a live vaccine. Immunity is conferred against several closely related poxviruses including smallpox and monkeypox.

A person with smallpox develops a characteristic rash.

For governments, the preparation of large amounts of a virus whose particles are fairly stable and long-lived, such as smallpox, is feasible. It is believed that the former Soviet Union had done so, as discussed earlier. The virus could be delivered using a medical nebulizer (see Fig. 22.14 ) or through the use of suicidal volunteers who would deliberately infect themselves and then travel to densely populated target areas. They would mingle with as many people as possible, by attending large events and utilizing mass transit. However, transmission requires close contact, and when a person is most contagious, he may be feeling far too ill to actually walk around in public.

Though many viruses are difficult to culture in large amounts and are unstable during storage, several others have been considered as possible biological warfare agents:

Ebola Virus

This electron micrograph depicts Ebola virus.

• ■ Flavivirus. Dengue fever and yellow fever are both caused by members of the Flavivirus family. Yellow fever is frequently lethal, whereas dengue is rarely fatal, but it is very painful and incapacitates its victims for several days. However, both are spread by insect bites, which would make their use as biological weapons difficult.
• ■ Arenavirus. An Arenavirus that appeared in the Lassa River region of Nigeria in the late 1960s causes Lassa hemorrhagic fever, which symptomatically resembles an Ebola infection. This segmented ssRNA virus has extremely high mortality and is typically spread by rodents.

Smallpox is the most likely virus to be used as a biological warfare agent. It is highly infectious, and the death rate may reach 30% to 40%. Other viruses with higher mortality rates may be prohibitively difficult to distribute.

Rust and Other Fungal Agents

Fungal agents perhaps may be most effectively used against staple crops, for instance, cereals and potatoes, which are an important part of the food supply. A wide variety of fungi exist that destroy these crops, such as rusts, smuts, and molds. Their spores are often highly infectious and easily dispersed by wind or rain, and in many cases there is no effective treatment.

Soybean rust and wheat stem rust are examples of pathogenic fungi that could destroy major crops. In addition to destruction of the crop, certain fungi may produce toxins. For example, when ergot grows on rye or other cereals, it produces a mixture of toxins that cause a syndrome referred to as ergotism, which can lead to convulsions, hallucinations, and even death ( Fig. 22.21 ). Some researchers believe that community ergot poisoning may have been responsible for the hysteria that led to the Salem witch trials.

Ergot on Quackgrass

Fungi such as Claviceps purpurea infect various grains such as wheat or rye as well as grasses such as quackgrass, shown here. The mature fungus forms purple to black bodies, called ergot bodies or sclerotia, where the grain would normally be positioned.

Another potential fungal agent is Aspergillus flavus , which infects cereals and legumes and produces the carcinogenic aflatoxin . Acute aflatoxin poisoning can cause liver damage and death, and chronic exposure can cause cancer. Herculean efforts are made to keep the food supply free of aflatoxin.

From the perspective of biological warfare, there are many advantages to using a fungal agent against crops. First, an entire crop might have to be screened even if only a small part was infected, causing major disruptions and economic losses. Second, dispersal could be rather easily accomplished by spraying fungal spores with a crop duster airplane over farmland. Alternatively, seeds could be infected, especially since many of them are imported to the United States and may be more easily accessed for contamination. Third, modern agriculture is particularly vulnerable to infection because large acres of genetically identical cultivars are often planted in high density. This lack of genetic variability could allow for an infection to spread rapidly. Finally, fungal agents that attack crops pose little danger to those using them.

The spores of highly infectious fungi could be used as biological warfare agents to target staple crops.

Purified Toxins

Another approach to biological warfare is to use purified toxins rather than a living infectious agent. A variety of toxins are known that may be purified in substantial quantities. Bacteria, primitive eukaryotes such as algae or fungi, higher plants, and animals all make toxins ( Table 22.2 ).

Toxins Relevant to Biowarfare

Botulinum toxin. The most toxic substance known is botulinum toxin . It is made by the anaerobic bacterium, Clostridium botulinum, and is the cause of botulism, a severe form of food poisoning. It has been proposed as a biological warfare agent but has actually found its most frequent application in cosmetics, under the name Botox. It is also used to treat a few clinical conditions in which a muscle relaxant is needed.

Botulinum toxin is a neurotoxin that blocks transmission of signals from nerves to muscles, thus causing muscular paralysis. The incredible potency of botulinum toxin is due to its enzymatic activity. It is a zinc protease that cleaves SNARE proteins in the neuromuscular junction that are required for release of the neurotransmitter acetylcholine. Death is generally due to paralysis of the lungs and respiratory failure ( Fig. 22.22 ).

Mechanism of Botulinum Toxin

Botulinum toxin disrupts the normal functioning of a neuromuscular junction by inhibiting the release of acetylcholine.

C. botulinum almost never causes infections but will grow in improperly canned food. Proper canning uses a pressure cooker to destroy the hardy spores produced by Clostridium . If the spores are not destroyed, they can germinate. After the bacteria die, they release botulinum toxin, which accumulates in the food. Merely 50 ng of botulinum toxin is enough to kill the average human. The toxin can, however, be destroyed by heating.

Terrorists of the Japanese cult Aum Shinrikyo, discussed previously, have attempted to use botulinum toxin. Aerosols were dispersed at various sites in Tokyo and at U.S. military installations in Japan on several occasions between 1990 and 1995. The attacks failed, mainly because the cult used strains of C. botulinum that failed to produce toxin. On the other hand, millions of people have willingly had extremely dilute preparations of botulinum toxin (Botox) injected into their face to eliminate wrinkles. The procedure works because botulinum toxin inhibits the muscle contraction responsible for causing them.

Ricin. Many higher plants make ribosome-inactivating proteins (RIPs) . These enzymes split the N-glycosidic bond between adenine and ribose from a specific sequence in the large-subunit ribosomal RNA. Clipping adenine from the rRNA totally inactivates the ribosome. A single RIP molecule is sufficient to inactivate all the ribosomes and kill a whole cell. Because RIPs are synthesized as precursor proteins that are fully processed only after exiting the plant cell’s cytoplasm, the toxin does not kill the plant. Intact ribosomes from different types of organisms differ greatly in their sensitivity to RIPs. Mammalian ribosomes (which contain 28S rRNA) are by far the most sensitive. On the other hand, the activity of many RIPs against bacterial ribosomes (which contain 23S rRNA) is low or negligible, and this has allowed the genes for some RIPs to be cloned and expressed in E. coli.

Like many bacterial toxins, ricin is a typical A-B toxin in which the A chain exhibits toxic enzymatic activity and the B chain mediates entry into the target cell. Ricin is lethal at around 3 μg/kg body weight, meaning that 300 μg should kill a large human. Ricin is extracted from the seeds of the castor bean plant, Ricinus communis ( Fig. 22.23 ). This plant is widely grown, both for ornamentation and on a large scale for castor oil production. Because of its widespread availability, high toxicity, stability, and lack of any antidote, there are several examples of the use of ricin as a biological weapon.

Seeds of the Castor Bean, Ricinus communis

Ricin achieved international notoriety in 1978 when the Bulgarian defector Georgi Markov was assassinated in a London street by ricin. The communist assassin wielded a modified umbrella that injected a hollow 0.6-mm-diameter metal sphere, filled with ricin, into Markov’s leg. In 1991, four members of the Patriots Council, an extremist group in Minnesota with an antigovernment and antitax ideology, purified ricin in a home laboratory. They were arrested for plotting to kill IRS and law enforcement agents with ricin. In late 2013, actress Shannon Richardson pleaded guilty for mailing letters containing ricin to President Barack Obama and New York City Mayor Michael Bloomberg in a scheme to frame her estranged husband. In a completely separate incident, in January 2014, James Dutschke also pleaded guilty to sending ricin to President Obama and other government officials with the intention of framing an Elvis Presley impersonator with whom he had a personal feud.

Abrin. Though less well known, abrin , which is also a ribosome-inactivating protein, is four times more toxic than ricin. Abrin is derived from the seeds of Abrus precatorius , commonly known as jequirity or rosary pea ( Fig. 22.24 ).

Seeds of the Rosary Pea, Abrus precatorius

The beautiful seeds of the rosary pea are highly toxic when the coat is damaged.

The beautiful seeds are widely used in jewelry, particularly rosary beads. However, the seeds are so toxic that, if broken or damaged, a small prick in the skin is sufficient to absorb a lethal dose of abrin. There have been reports of abrin poisoning in jewelry makers, as well as in individuals who ingested seeds, but there are no known instances of abrin being used as a biological weapon.

Conotoxin. Cone snails are predators that use a venom cocktail containing at least 100 different conotoxins to paralyze and kill their prey. The most dangerous cone snail to humans, Conus geographus , stabs fish with a venom-filled “harpoon” located in its proboscis ( Fig. 22.25 ).

Cone snail, Conus geographus

The cone snail produces highly toxic venom.

Death from the sting of a cone snail is largely due to α-conotoxins, which cause muscle paralysis leading to respiratory arrest. Other toxins may trigger cardiovascular collapse. Symptomatically, α-conotoxins resemble botulinum toxin, although the mechanism of action is different. Because most conotoxins are short peptides 10–30 amino acids in length, the concern from a biological warfare perspective is not that a government or terrorist would harvest venom from cone snails but that the toxins would be chemically synthesized.

Purified toxins are possible biological warfare agents. Natural toxins can be isolated from bacteria, plants, and animals, but other toxins could be chemically synthesized. Botulinum toxin disrupts the neuromuscular junction and is the most potent toxin known. Ricin and abrin are ribosome-inactivating proteins that are made by certain plants.

Enhancing Biological Warfare Agents with Biotechnology

It is often suggested that genetic engineering could be used to create more dangerous versions of infectious agents. Although there is some truth to this assertion, consider the following:

Suppose a bioterrorist tries to genetically modify a harmless laboratory bacterium, such as E. coli . The bacteria could be engineered to go “under cover” when they enter the human body, hiding from the immune system. Additionally, the bacteria could be programmed to rebuff immune cells by injecting them with toxins, and other genes could be added for ripping vital supplies of iron away from blood cells. Finally, the bacteria could be modified to be highly infectious. Such a biological agent would make for a fearsome weapon.

Unfortunately, this bacterium already exists. It is called Yersinia pestis . It is the agent of bubonic plague and is still endemic in many parts of the world, including China, India, Madagascar, and the United States. Instead of devoting years to genetically engineer a lethal biological weapon, a bioterrorist could simply isolate one of Mother Nature’s very own products. The “improvement” of infectious diseases by genetic engineering, therefore, is probably a minor threat.

Still, genetic engineering of biological warfare agents is theoretically possible, so we briefly consider the issue here.

Engineering Pathogens to Be More Lethal

The Soviet germ warfare facility is known to have modified smallpox virus and generated a variety of artificial mutants and hybrids. The details are largely unavailable. However, recent experiments with mousepox (Ectromelia virus) have given disturbing results. Mousepox is related to smallpox, but it only infects mice. Its virulence varies greatly depending on the strain of mouse. Genetically resistant mice rely on cell-mediated immunity, rather than antibodies. Natural killer (NK) cells and cytotoxic T cells destroy cells infected with mousepox virus, thus clearing the virus from the body.

Researchers modified mousepox virus by inserting the human gene for the cytokine interleukin-4 (IL-4). IL-4 is known to stimulate the division of B cells, which synthesize antibodies. The rationale for engineering the virus was that IL-4 would stimulate the production of antibodies and lead to an improved and more balanced immune response. What actually happened was the opposite of what was expected: the creation of a virus with vastly greater virulence. Not only did it kill all of the genetically resistant mice, but it also killed 50% of mice that had been vaccinated against mousepox. The expression of excess IL-4 suppressed the NK cells and cytotoxic T cells. Furthermore, it failed to increase the antibody response. The reasons are not fully understood, but they do serve as a reminder that the immune system is under extremely complex control.

Similar results have been seen with strains of Vaccinia virus, which is used for vaccination against smallpox. Whether insertion of IL-4 or other immune regulators into smallpox itself would lead to increased virulence by undermining the immune response is unknown. pox- viruses already possess genes designed to protect the virus by interfering with the action of NK cells and cytotoxic T cells ( Fig. 22.26 ). These are the cytokine response modifier ( crm ) genes, and they vary in effectiveness among different poxviruses. One reason smallpox is so virulent may be that it already subverts the body’s cell-mediated immune response. In this case, adding IL-4 would not be expected to increase virulence.

Poxvirus Immune Evasion

Poxvirus deploys many different proteins to prevent the infected cell from being attacked by the host’s immune system.

Creating Camouflaged Viruses

With genetic engineering, it is also possible to hide a potentially dangerous virus inside a harmless bacterium. This strategy is already used in nature when bacteriophages insert their genomes into bacterial chromosomes or plasmids and later re-emerge to infect other hosts.

Theoretically, cloning the entire genome of a small animal or plant virus into a bacterial plasmid could create a biological weapon. Larger viruses could be accommodated with bacterial or yeast artificial chromosomes. In the case of RNA viruses, a cDNA copy of the virus genome must first be generated by reverse transcriptase before cloning it into a bacterial vector. Any virus containing a poison sequence , a base sequence that is not stably maintained on bacterial plasmids, could perhaps be cloned as separate fragments. Such a strategy works for yellow fever virus, but a complete, functional cDNA requires ligation of the fragments in vitro .

Many cell types, both bacterial and eukaryotic, can take up DNA or RNA under certain circumstances by transformation. Consequently, the naked nucleic acid genomes of many viruses, both DNA and RNA, are infectious even in the absence of their protein capsids or envelopes. Thus, once a viral genome is cloned, the DNA molecule containing it may itself be infectious. Alternatively, the cDNA version of some RNA viruses can successfully infect host cells and give rise to a new crop of RNA-containing virus particles. This has been demonstrated for RNA viruses such as poliovirus, influenza, and coronavirus.

The cleverest strategy for generating an RNA virus is to clone the cDNA version of its genome onto a bacterial plasmid downstream of a strong promoter ( Fig. 22.27 ). The natural RNA version of the viral genome will be generated by transcription. When induced, the bacterial cell would generate a large number of infectious viral particles. A dangerous human RNA virus loaded into a harmless intestinal bacterium under the control of a promoter designed to respond to conditions inside the intestine could pose a formidable threat.

Genetically engineering biological warfare agents to make them deadlier is a minor threat since many naturally occurring microbes are already very dangerous. However, certain poxviruses have been modified to become more virulent. Inserting viral DNA into plasmids carried by harmless bacteria could create camouflaged viruses.

Expression of Cloned RNA Virus

Cloning an RNA virus requires making a double-stranded DNA copy using reverse transcriptase. The cDNA is inserted into an appropriate bacterial plasmid and transformed into bacterial cells. To control the expression of the viral DNA, a strong promoter is placed upstream of the viral cDNA. If the promoter is inducible, when the bacteria are given the appropriate stimulus, the viral cDNA will be expressed, resulting in production of viral particles that could infect many people.

Detection of Biological Warfare Agents

In the laboratory, some pathogenic bacteria grow slowly or not at all. This may be because the microbe has fastidious nutrient requirements or is otherwise difficult to culture outside its host organism. However, thanks to advances in biotechnology, infectious microbes can be identified using a variety of different techniques.

Molecular Diagnostics

Rather than attempting to grow and identify disease-causing agents using classical microbiological techniques, molecular diagnostics analyzes molecules; typically DNA, but RNA, proteins, and volatile organic compounds can also be used. (Other diagnostic methods involve the use of antibody technology and are discussed in Chapter 6.) Molecular techniques have the advantage of being quicker, more accurate, and more sensitive.

One diagnostic method is called fluorescent in situ hybridization (FISH; for details see Chapter 3). Biopsies or other patient samples are directly probed with fluorescent DNA oligonucleotides specific to a pathogen of interest. If the pathogen is present, the probe binds to the complementary DNA in its chromosome and the fluorescence can be visualized under a microscope. A new innovation, called peptide nucleic acid (PNA), replaces the negatively charged sugar-phosphate backbone of DNA with a neutral peptide backbone. Probes made of PNA bind complementary DNA more tightly and enter bacterial cells more easily ( Fig. 22.28 ).

PNA FISH Probe

The yeast Candida albicans is detected in a blood culture using fluorescent in situ hybridization (FISH) with a peptide nucleic acid (PNA) probe. Fluorescence microscopy; original magnification 500x.

Most other methods based on DNA detection involve extracting DNA from a sample followed by amplification via PCR. Because primers can be designed to amplify DNA sequences unique to a particular pathogen, PCR itself can serve as a diagnostic tool. The advantages of PCR are that it theoretically requires only a single molecule of target DNA and works on microbes that cannot be cultured in the laboratory. The downside is that PCR is susceptible to contamination and false positives. A variant of PCR (see Chapter 4), called randomly amplified polymorphic DNA (RAPD), can be used to distinguish different strains of the same bacterial species. This capability is useful in epidemiology for tracking the spread of infectious disease.

Additionally, every species of microorganism has a different small-subunit ribosomal RNA (SSU rRNA) sequence (16S rRNA in bacteria and 18S rRNA in eukaryotes). Thus, if a patient has an unknown infection, clinicians can use PCR to amplify the gene encoding the microbe’s SSU rRNA. Primers that recognize the conserved region of SSU rRNA are used to amplify the gene. The PCR fragment is then sequenced and compared with a database of known DNA sequences.

Another technique that generally relies on SSU rRNA is checkerboard hybridization . This allows multiple bacteria to be detected and identified simultaneously in a single sample. A series of probes corresponding to different bacteria are applied in horizontal lines across a hybridization membrane ( Fig. 22.29 ). PCR is used to amplify a portion of the SSU rRNA gene from clinical samples, which may contain a mixture of pathogens. The PCR fragments are then labeled with a fluorescent dye and applied vertically to the membrane. After denaturation and annealing to allow hybridization, the membrane is washed to remove unbound DNA. Those samples that hybridize to the probes appear as bright fluorescent spots.

Checkerboard Hybridization

Probes corresponding to 16S rRNA for each candidate bacterium are attached to a membrane filter in long horizontal stripes (one candidate per stripe). DNA from patient samples is extracted and amplified by PCR using primers for 16S rRNA. The PCR fragments are tagged with a fluorescent dye and applied in vertical stripes. Each sample is thus exposed to each probe. Wherever a 16S PCR fragment matches a 16S probe, the two bind, forming a strong fluorescent signal where the two stripes intersect.

A potentially revolutionary technology called PLEX-ID has been developed by Abbott Laboratories. It combines traditional PCR with mass spectrometry to identify unknown microbes in patient samples. DNA is extracted and many different sets of primers are used to amplify various target sequences. The fragments are then analyzed with a mass spectrometer to determine their mass. From this information, the DNA sequence can be deduced and the pathogen identified. PLEX-ID can make a diagnosis in 8 hours.

In the future, it may be possible to diagnose disease using an “electronic nose.” As the name implies, the device detects volatile organic compounds that are released by pathogens or by the body in certain diseased conditions.

Biosensors are devices for the detection and measurement of reactions that rely on a biological mechanism ( Fig. 22.30 ). Biosensors have been traditionally used in medical diagnostics and in food and environmental analysis. By far the biggest use has been the clinical monitoring of glucose levels in diabetics using the enzyme glucose oxidase.

Biosensors, in general, share a common design. A highly specific biological receptor molecule detects or interacts with a target molecule of interest, for instance, a biological warfare agent. A signal is generated, processed, and displayed for the user.

There is growing interest today in using biosensors to detect biological warfare agents. Placing biosensors in high trafficked areas, such as in malls or subway stations, could allow for continuous surveillance. Additionally, handheld devices giving a rapid response at the site of a possible attack would be highly useful. Several proposals exist that would use specific antibodies or antibody fragments as detectors for biological warfare agents (see Chapter 6 for antibody engineering).

B cells carry antibodies specific for one antigen, so one proposal is to use whole B cells in a biosensor. When an antigen binds to the antibody on the surface of a B cell, it triggers a signal cascade. Engineered B cells have been made that express aequorin , a light-emitting protein from the luminescent jellyfish Aequorea victoria. Aequorin emits blue light when triggered by calcium ions ( Fig. 22.31 ). Living jellyfish actually produce flashes of blue light, which are transduced to green by the famous green fluorescent protein (GFP).

Light Emission by Aequorin

Aequorin, from Aequorea victoria, emits blue light when provided with its substrate, coelenterazine, plus oxygen and calcium. The enzyme binds to aequorin via the oxygen; and when calcium is present, the complex emits blue light, degrades the substrate to coelenteramide, and releases carbon dioxide.

In a biosensor, when a B cell detected a disease agent (or any specific antigen), calcium ions would flood into the cell due to activation of a signal cascade ( Fig. 22.32 ). This in turn triggers light emission by aequorin. The light emitted is detected by a sensitive charge-coupled device (CCD) detector. This approach could detect 5 to 10 particles of a biological warfare agent. Approximately 10,000 B cells specific to different pathogens could be assembled in array fashion onto a chip placed inside the biosensor.

B-Cell Optical Biosensor

Expressing aequorin in a B cell would provide a detection system for B-cell activation. When a trigger molecule, such as a biological warfare agent, binds to receptors on the B cell, the calcium channels are opened and calcium floods the cell. The high calcium levels would activate aequorin to emit blue light. A charge-coupled device (CCD) would measure the photon emissions and warn the user of a biological agent.

Another scheme developed by the Ambri Corporation of Australia uses antibody fragments mounted on an artificial biological membrane, which is attached to a solid support covered by a gold electrode layer. Channels for sodium ions are incorporated into the membrane. When the ion channels are open, sodium ions flow across the membrane and a current is generated in the gold electrode. The ion channels consist of two modules, each spanning half the membrane. When top and bottom modules are united, the ion channel is open. When the top module is pulled away, the ion channel cannot operate. Binding of biological warfare agents by the antibody fragments separates the two halves of the channels, which in turn affects the electrical signal ( Fig. 22.33 ).

Diagnosing pathogenic bacteria with molecular techniques, particularly using the genes encoding ribosomal RNA sequences, is faster and more sensitive than traditional microbiological methods. Biosensors use biological components themselves to monitor for suspicious biomolecules.

Antibody Ion-Channel Biosensor

Antibody fragments that bind specific biological agents can be engineered and tethered to a fixed location on an artificial membrane. Another molecule of the same antibody fragment is tethered to a sodium channel. The artificial membrane is carried on a gold-coated solid support that acts as an electrode. This detects sodium ions that pass through the ion channel. When a biological agent is present, the antibody fragments bind it, pulling the top half of the sodium channel out of alignment with the bottom half. Sodium ions no longer pass to the gold electrode, decreasing the signal.

Biological warfare has been around since life first evolved. Humans are most concerned about the biological warfare directed at us, including infectious diseases and the ability of microbes to evolve resistance to antibacterial agents. Although this development is worrisome, new strategies and technologies are being developed to fight back against the growing problem of antibiotic resistance.

Humans have often attempted to use biological agents in warfare, although with little overall success so far. Several highly virulent infectious agents including anthrax, plague, and smallpox, as well as certain biological toxins such as ricin and abrin, are regarded as likely biological warfare agents. Whether or not genetic engineering can create “improved” bioweapons is as yet uncertain. Developing quicker ways to detect and diagnose microbes is an active area of research.

End-of-Chapter Questions

• a. insect cells
• b. human cells
• c. other bacterial cells
• d. protozoa
• e. all of the above
• a. Siderophores are a good target because they do not exist in humans, and thus the side effects would be diminished.
• b. Disruption of quorum sensing causes bacteria to produce more antibiotic-resistant biofilms.
• c. Alkyl- and aryl-mannose derivatives bind to FimH adhesins and enhance attachment to the natural receptor.
• d. Phage therapy increases the virulence of the bacteria due to transduction.
• e. Production of aflatoxin inhibits fungal agents from growing on cereals.
• a. dispersal
• b. persistence of the agent
• c. incubation time
• d. storage and preparation of the agent
• a. It should be able to be produced economically.
• b. It should consistently produce death, disability, or damage.
• c. It should be stable from production through delivery.
• d. It should be easy to disseminate quickly and effectively.
• e. All of the above are requirements for biological agents.
• b. bacteria
• c. pathogenic eukaryotes
• d. pathogenic fungi
• e. none of the above
• c. amoebic dysentery
• d. smallpox
• a. 16S rRNA sequencing
• c. 23s rRNA sequencing
• d. gene expression profiles
• b. person-to-person
• a. Variola major
• b. monkeypox
• c. Variola minor
• d. Vaccinia virus
• a. flaviviruses
• b. poxviruses
• c. filoviruses
• d. variola viruses
• e. arenaviruses
• a. aflatoxin
• c. yersiniabactin
• d. anthracimycin
• a. inactivation of transcription
• b. inactivation of rRNA
• c. activation of the apoptosis pathway
• d. inactivation of the immune system
• e. creation of pores in cell walls
• c. pathogenic fungi spores
• a. monkeypox
• b. smallpox
• c. chickenpox
• d. mousepox
• e. camelpox
• a. by antibodies that are connected to components to give electrical signals or trigger light emission
• b. by isolating the pathogen directly from the sample
• c. biosensors detect antibodies against specific pathogens, similar to a Western blot
• d. by using PCR to amplify variable regions of the pathogen’s genome
• a. black silicon
• b. nanopillars
• c. nanocarpets
• d. polymers of esters and cyclic hydrocarbons
• a. inhibits the release of acetylcholine
• b. activates the release of acetylcholine
• c. causes muscle contraction
• d. mimics the action of acetylcholine
• e. stimulates acetylcholine receptors
• d. SNP analysis

Further Reading

• Abedon S.T., Kuhl S.J., Blasdel B.G., Kutter E.M. Phage treatment of human infections. Bacteriophage. 2011; 1 :66–85. [ PMC free article ] [ PubMed ] [ Google Scholar ]
• Anderson P.D., Bokor G. Conotoxins: potential weapons from the sea. Journal of Bioterrorism and Biodefense. 2012; 3 :120. [ Google Scholar ]
• Centers for Disease Control and Prevention . 2013. Antibiotic Resistance Threats in the United States. 2013. [ Google Scholar ]
• Croddy E. Copernicus Books; New York City, NY: 2002. Chemical and Biological Warfare: A Comprehensive Survey for the Concerned Citizen. [ Google Scholar ]
• Domaradskij I.V., Orent L.W. Achievements of the Soviet biological weapons programme and implications for the future. Revue Scientifique et Technique (International Office of Epizootics) 2006; 25 :153–161. [ PubMed ] [ Google Scholar ]
• Dublanchet A., Bourne S. The epic of phage therapy. Canada Journal of Infectious Disease and Medical Microbiology. 2007; 18 :15–18. [ PMC free article ] [ PubMed ] [ Google Scholar ]
• Fang Y., Rowland R.R., Roof M., Lunney J.K., Christopher-Hennings J., Nelson E.A. A full-length cDNA infectious clone of North American type 1 porcine reproductive and respiratory syndrome virus: expression of green fluorescent protein in the Nsp2 region. Journal of Virology. 2006; 80 :11447–11455. [ PMC free article ] [ PubMed ] [ Google Scholar ]
• Halverson K.M., Panchal R.G., Nguyen T.L., Gussio R., Little S.F., Misakian M., Bavari S., Kasianowicz J.J. Anthrax biosensor, protective antigen ion channel asymmetric blockade. The Journal of Biological Chemistry. 2005; 280 :34056–34062. [ PubMed ] [ Google Scholar ]
• Jolley K.A., Brehony C., Maiden M.C. Molecular typing of meningococci: Recommendations for target choice and nomenclature. FEMS Microbiology Reviews. 2007; 31 :89–96. [ PubMed ] [ Google Scholar ]
• Li Y., Sherer K., Cui X., Eichacker P.Q. New insights into the pathogenesis and treatment of anthrax toxin-induced shock. Expert Opinion on Biological Therapy. 2007; 7 :843–854. [ PubMed ] [ Google Scholar ]
• Muldrew K.L. Molecular diagnostics of infectious diseases. Current Opinion in Pediatrics. 2009; 21 :102–111. [ PubMed ] [ Google Scholar ]
• Neumann G., Kawaoka Y. Reverse genetics systems for the generation of segmented negative-sense RNA viruses entirely from cloned cDNA. Current Topics in Microbiology and Immunology. 2004; 283 :43–60. [ PubMed ] [ Google Scholar ]
• Osborne S.L., Latham C.F., Wen P.J., Cavaignac S., Fanning J., Foran P.G., Meunier F.A. The Janus faces of botulinum neurotoxin: sensational medicine and deadly biological weapon. Journal of Neuroscience Research. 2007; 85 :1149–1158. [ PubMed ] [ Google Scholar ]
• Palomino J.C. Newer diagnostics for tuberculosis and multi-drug resistant tuberculosis. Current Opinion in Pulmonary Medicine. 2006; 12 :172–178. [ PubMed ] [ Google Scholar ]
• Pastagia M., Schuch R., Fischetti V.A., Huang D.B. Lysins: the arrival of pathogen-directed anti-infectives. Journal of Medical Microbiology. 2013; 62 :1506–1516. [ PubMed ] [ Google Scholar ]
• Paterson R.R. Fungi and fungal toxins as weapons. Mycological Research. 2006; 110 :1003–1010. [ PubMed ] [ Google Scholar ]
• Pinton P., Rimessi A., Romagnoli A., Prandini A., Rizzuto R. Biosensors for the detection of calcium and pH. Methods in Cell Biology. 2007; 80 :297–325. [ PubMed ] [ Google Scholar ]
• Prentice M.B., Rahalison L. Plague. Lancet. 2007; 369 :1196–1207. [ PubMed ] [ Google Scholar ]
• Roxas-Duncan V.I., Smith L.A. Of beans and beads: ricin and abrin in bioterrorism and biocrime. Journal of Bioterrorism and Biodefense. 2012 S7, 002. [ Google Scholar ]
• Schrallhammer M. The killer trait of Paramecium and its causative agents. Palaeodiversity. 2010; 3 (Suppl):79–88. [ Google Scholar ]
• Simon J.D. Why the bioterrorism skeptics are wrong. Journal of Bioterrorism and Biodefense. 2011 S2, 001. [ Google Scholar ]
• Sliva K., Schnierle B. From actually toxic to highly specific—novel drugs against poxviruses. Virology Journal. 2007; 4 :8. [ PMC free article ] [ PubMed ] [ Google Scholar ]
• Stirpe F. Ribosome-inactivating proteins. Toxicon. 2004; 44 :371–383. [ PubMed ] [ Google Scholar ]
• Trull M.C., du Laney T.V., Dibner M.D. Turning biodefense dollars into products. Nature Biotechnology. 2007; 25 :179–184. [ PMC free article ] [ PubMed ] [ Google Scholar ]
• van Belkum A. Tracing isolates of bacterial species by multilocus variable number of tandem repeat analysis (MLVA) FEMS Immunology and Medical Microbiology. 2007; 49 :22–27. [ PubMed ] [ Google Scholar ]
• Yamanaka K. Direct cloning and refactoring of a silent lipopeptide biosynthetic gene cluster yields the antibiotic taromycin A. PNAS. 2014; 11 :1957–1962. [ PMC free article ] [ PubMed ] [ Google Scholar ]

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Collection  15 July 2019

Top 50: Life and Biological Sciences

We are pleased to share with you the 50 most read  Nature Communications life and biological sciences articles* published in 2018. Featuring authors from around the world, these papers highlight valuable research from an international community.

Browse all Top 50 subject area collections here .

*Based on data from  altmetric.com , covering January-December 2018

Embryos and embryonic stem cells from the white rhinoceros

The Southern (SWR) and Northern (NWR) are two subspecies of the White Rhinoceros with the NWR being almost extinct. Here, using assisted reproduction technology, the authors produce and cryopreserve SWR purebred and NWR-SWR hybrid embryos developed to the blastocyst stage, and also generate embryonic stem cell lines, in an attempt to save genes of the NWR.

• Thomas B. Hildebrandt
• Robert Hermes
• Cesare Galli

Scutoids are a geometrical solution to three-dimensional packing of epithelia

Cell arrangement in the plane of epithelia is well studied, but its three-dimensional packing is largely unknown. Here the authors model curved epithelia and predict that cells adopt a geometrical shape they call “scutoid”, resulting in different apical and basal neighbours, and confirm the presence of scutoids in curved tissues.

• Pedro Gómez-Gálvez
• Pablo Vicente-Munuera
• Luis M. Escudero

Similar neural responses predict friendship

Though we are often friends with people similar to ourselves, it is unclear if neural responses to perceptual stimuli are also similar. Here, authors show that the similarity of neural responses evoked by a range of videos was highest for close friends and decreased with increasing social distance.

• Carolyn Parkinson
• Adam M. Kleinbaum
• Thalia Wheatley

Study of 300,486 individuals identifies 148 independent genetic loci influencing general cognitive function

Cognitive function is associated with health and important life outcomes. Here, the authors perform a genome-wide association study for general cognitive function in 300,486 individuals and identify genetic loci that implicate neural and cell developmental pathways in this trait.

• Gail Davies
• Ian J. Deary

Wing bone geometry reveals active flight in Archaeopteryx

Archaeopteryx had a mix of traits seen in non-flying dinosaurs and flying birds, leading to debate on whether it had powered flight. Here, Voeten et al. compare wing bone architecture from Archaeopteryx and both flying and non-flying archosaurs, supporting that Archaeopteryx had powered flight but with a different stroke than that of modern birds.

• Dennis F. A. E. Voeten
• Sophie Sanchez

Hunting regulation favors slow life histories in a large carnivore

Hunting and harvesting are generally expected to select for faster life histories in the exploited species. Here, the authors analyse data from a hunted population of brown bears in Sweden and show that regulations protecting females with dependent young lead hunting to favor prolonged maternal care.

• Joanie Van de Walle
• Gabriel Pigeon
• Fanie Pelletier

Closed-loop stimulation of temporal cortex rescues functional networks and improves memory

Memory lapses can occur due to ineffective encoding, but it is unclear if targeted brain stimulation can improve memory performance. Here, authors use a closed-loop system to decode and stimulate periods of ineffective encoding, showing that stimulation of lateral temporal cortex can enhance memory.

• Youssef Ezzyat
• Paul A. Wanda
• Michael J. Kahana

Genome-wide study of hair colour in UK Biobank explains most of the SNP heritability

Natural hair colour in Europeans is a complex genetic trait. Here, the authors carry out a genome-wide association study using UK BioBank data, suggesting that in combination with pigmentation genes, variants with roles in hair texture and growth can affect hair colouration or our perception of it.

• Michael D. Morgan
• Erola Pairo-Castineira
• Ian J. Jackson

Diffusion markers of dendritic density and arborization in gray matter predict differences in intelligence

Previous studies suggest that individual differences in intelligence correlate with circuit complexity and dendritic arborization in the brain. Here the authors use NODDI, a diffusion MRI technique, to confirm that neurite density and arborization are inversely related to measures of intelligence.

• Christoph Fraenz
• Rex E. Jung

Industrial brewing yeast engineered for the production of primary flavor determinants in hopped beer

Production of aromatic monoterpene molecules in hop flowers is affected by genetic, environmental, and processing factors. Here, the authors engineer brewer’s yeast for the production of linalool and geraniol, and show pilot-scale beer produced by engineered strains reconstitutes some qualities of hop flavor.

• Charles M. Denby
• Rachel A. Li
• Jay D. Keasling

A bony-crested Jurassic dinosaur with evidence of iridescent plumage highlights complexity in early paravian evolution

A number of paravian dinosaurs have been described from the Jurassic Yanliao biota, but these have tended to be morphologically similar to Archaeopteryx . Here, Hu. describe the new paravian dinosaur, Caihong juji gen. et sp. nov., which possesses a suite of unusual skeletal and feather characteristics.

• Julia A. Clarke

Single-dose testosterone administration increases men’s preference for status goods

Testosterone is believed to be involved in social rank-related behavior. Here, the authors show that one dose of testosterone increases men’s preference for “high status” goods and brands, suggesting a role for testosterone in modern consumer behavior in men.

• H. Plassmann

Development of an oral once-weekly drug delivery system for HIV antiretroviral therapy

Poor adherence to daily antiretrovirals can significantly affect treatment efficacy, but oral long-acting antiretrovirals are currently lacking. Here, the authors develop a once-weekly oral dosage form for anti-HIV drugs, assess its pharmacokinetics in pigs, and model its impact on viral resistance and disease epidemics.

• Ameya R. Kirtane
• Omar Abouzid
• Giovanni Traverso

Smartphone app for non-invasive detection of anemia using only patient-sourced photos

Anemia has a global prevalence of over 2 billion people and is diagnosed via blood-based laboratory test. Here the authors describe a smartphone app that can estimate hemoglobin levels and detect anemia by analyzing pictures of fingernail beds taken with a smartphone and without the need of any external equipment.

• Robert G. Mannino
• David R. Myers
• Wilbur A. Lam

Sleep loss causes social withdrawal and loneliness

Loneliness markedly increases mortality and morbidity, yet the factors triggering loneliness remain largely unknown. This study shows that sleep loss leads to a neurobehavioral phenotype of human social separation and loneliness, one that is transmittable to non-sleep-deprived individuals.

• Eti Ben Simon
• Matthew P. Walker

Gender differences in individual variation in academic grades fail to fit expected patterns for STEM

Men are over-represented in the STEM (science, technology, engineering and mathematics) workforce even though girls outperform boys in these subjects at school. Here, the authors cast doubt on one leading explanation for this paradox, the ‘variability hypothesis’.

• R. E. O’Dea
• S. Nakagawa

The spread of low-credibility content by social bots

Online misinformation is a threat to a well-informed electorate and undermines democracy. Here, the authors analyse the spread of articles on Twitter, find that bots play a major role in the spread of low-credibility content and suggest control measures for limiting the spread of misinformation.

• Chengcheng Shao
• Giovanni Luca Ciampaglia
• Filippo Menczer

Tailed giant Tupanvirus possesses the most complete translational apparatus of the known virosphere

Giant viruses are the largest viruses of the known virosphere and their genetic analysis can provide insights into virus evolution. Here, the authors discover Tupanvirus, a unique giant virus that has an unusually long tail and contains the largest translational apparatus of the known virosphere.

• Jônatas Abrahão
• Lorena Silva
• Bernard La Scola

Genome-wide meta-analysis implicates mediators of hair follicle development and morphogenesis in risk for severe acne

Acne vulgaris is a chronic inflammation of the skin, the genetic basis of which is incompletely understood. Here, Petridis et al. perform GWAS and meta-analysis for acne in 26,722 individuals and identify 12 novel risk loci that implicate structure and maintenance of the skin in severe acne risk.

• Christos Petridis
• Alexander A. Navarini
• Michael A. Simpson

Patterns of island change and persistence offer alternate adaptation pathways for atoll nations

Inundation and erosion could make many atoll islands uninhabitable over the next century. Here the authors present an analysis of change in the atoll nation of Tuvalu that shows a 2.9% increase in land area over the past four decades, with 74% of islands increasing in size, despite rising sea levels.

• Paul S. Kench
• Murray R. Ford
• Susan D. Owen

Blood–brain barrier opening in Alzheimer’s disease using MR-guided focused ultrasound

Magnetic resonance-guided focused ultrasound with injected microbubbles has been used to temporarily open the blood–brain barrier (BBB) in animal models of Alzheimer's disease (AD). Here, the authors use this technology to non-invasively open the BBB in 5 patients with mild-to-moderate AD in a phase I trial, and show that the procedure is safe.

• Nir Lipsman
• Sandra E. Black

Cultural hitchhiking and competition between patrilineal kin groups explain the post-Neolithic Y-chromosome bottleneck

A population bottleneck 5000-7000 years ago in human males, but not females, has been inferred across several African, European and Asian populations. Here, Zeng and colleagues synthesize theory and data to suggest that competition among patrilineal kin groups produced the bottleneck pattern.

• Tian Chen Zeng
• Marcus W. Feldman

Caffeine-inducible gene switches controlling experimental diabetes

Control of transgene expression should ideally be easy and with minimal side effects. Here the authors present a synthetic biology-based approach in which the caffeine in coffee regulates a genetic circuit controlling glucagon-like peptide 1 expression in diabetic mice.

• Daniel Bojar
• Leo Scheller
• Martin Fussenegger

Assembly of 913 microbial genomes from metagenomic sequencing of the cow rumen

Microbes in the cow rumen are crucial for the breakdown of plant material. Here, Stewart et al. assemble over 900 bacterial and archaeal genomes from the cow rumen microbiome, revealing new species and genes encoding enzymes with potential roles in carbohydrate metabolism.

• Robert D. Stewart
• Marc D. Auffret
• Mick Watson

Genome-wide association study of depression phenotypes in UK Biobank identifies variants in excitatory synaptic pathways

The UK Biobank provides data for three depression-related phenotypes. Here, Howard et al. perform a genome-association study for broad depression, probable major depressive disorder (MDD) and hospital record-coded MDD in up to 322,580 UK Biobank participants which highlights excitatory synaptic pathways.

• David M. Howard
• Mark J. Adams
• Andrew M. McIntosh

Fungal networks shape dynamics of bacterial dispersal and community assembly in cheese rind microbiomes

Interactions with other microbes may inhibit or facilitate the dispersal of bacteria. Here, Zhang et al. use cheese rind microbiomes as a model to show that physical networks created by filamentous fungi can affect the dispersal of motile bacteria and thus shape the diversity of microbial communities.

• Yuanchen Zhang
• Erik K. Kastman
• Benjamin E. Wolfe

Epidemiology is a science of high importance

Epidemiology dates back to the Age of Pericles in 5th Century B.C., but its standing as a ‘true’ science in 21st century is often questioned. This is unexpected, given that epidemiology directly impacts lives and our reliance on it will only increase in a changing world.

A low-gluten diet induces changes in the intestinal microbiome of healthy Danish adults

Gluten-free diets are increasingly common in the general population. Here, the authors report the results of a randomised cross-over trial involving middle-aged, healthy Danish adults, showing evidence that a low-gluten diet leads to gut microbiome changes, possibly due to variations in dietary fibres.

• Lea B. S. Hansen
• Henrik M. Roager
• Oluf Pedersen

In utero nanoparticle delivery for site-specific genome editing

The correction of genetic defects in utero could allow for improved outcomes of gene therapy. Here, the authors demonstrate safe delivery of nanoparticles to fetal mouse tissues, and show that nanoparticles containing peptide nucleic acids to edit the beta-globin gene are effective in a mouse model of beta-thalassemia.

• Adele S. Ricciardi
• Raman Bahal
• W. Mark Saltzman

The effects of death and post-mortem cold ischemia on human tissue transcriptomes

RNA levels in post-mortem tissue can differ greatly from those before death. Studying the effect of post-mortem interval on the transcriptome in 36 human tissues, Ferreira et al. find that the response to death is largely tissue-specific and develop a model to predict time since death based on RNA data.

• Pedro G. Ferreira
• Manuel Muñoz-Aguirre
• Roderic Guigó

Gimap5-dependent inactivation of GSK3β is required for CD4 + T cell homeostasis and prevention of immune pathology

Loss of function GIMAP5 mutation is associated with lymphopenia, but how it mediates T cell homeostasis is unclear. Here the authors study Gimap5 −/− mice and a patient with GIMAP5 deficiency to show how this GTPAse negatively regulates GSK3β activity to prevent DNA damage and cell death.

• Andrew R. Patterson
• Mehari Endale
• Kasper Hoebe

3D virtual reconstruction of the Kebara 2 Neandertal thorax

How different Neandertal morphology was from that of modern humans has been a subject of long debate. Here, the authors develop a 3D virtual reconstruction of the thorax of an adult male Neandertal, showing similar size to modern humans, yet with greater respiratory capacity due to its different shape.

• Asier Gómez-Olivencia
• Alon Barash

Exercise induces new cardiomyocyte generation in the adult mammalian heart

The adult mammalian heart has a limited cardiomyogenic capacity. Here the authors show that intensive exercise leads to a 4.6-fold increase in murine cardiomyocyte proliferation requiring the expression of miR-222, and that exercise induces an extended cardiomyogenic response in the murine heart after infarction.

• Carolin Lerchenmüller
• Anthony Rosenzweig

Double-layered protein nanoparticles induce broad protection against divergent influenza A viruses

Relatively well conserved domains of influenza A virus (IAV) proteins are potential candidates for the development of a universal IAV vaccine. Here, Deng et al . combine two such conserved antigens (M2e and HA stalk) in a double-layered protein nanoparticle and show that it protects against divergent IAVs in mice.

• Teena Mohan
• Bao-Zhong Wang

Intellectual synthesis in mentorship determines success in academic careers

While successful mentors tend to train successful students in academic career, it’s unclear how mentorship determines chances of a success in a trainee. Here, Liénard and colleagues analyze approximately 20 K mentor/trainee relationships in life sciences, and find that success of trainees is associated with an intellectual synthesis between their mentors’ research.

• Jean F. Liénard
• Titipat Achakulvisut
• Stephen V. David

Effective weight control via an implanted self-powered vagus nerve stimulation device

Developing new technologies for the neuromodulation of the vagus nerve can enable therapeutic strategies for body weight control in obese patients. Here, the authors present a battery-free self-powered implantable vagus nerve stimulation system that electrically responds to stomach movement.

• Xudong Wang

Olfactory receptor OR2AT4 regulates human hair growth

Increasing evidence suggest that olfactory receptors can carry additional functions besides olfaction. Here, Chéret et al. show that stimulation of the olfactory receptor ORT2A4 by the odorant Sandalore ® stimulates growth of human scalp hair follicles ex vivo, suggesting the use of ORT2A4-targeting odorants as hair growth-promoting agents.

• Jérémy Chéret
• Marta Bertolini

A diminutive perinate European Enantiornithes reveals an asynchronous ossification pattern in early birds

Fossil juvenile Mesozoic birds are exceedingly rare and can provide important insight into the early evolution of avian development. Here, Knoll et al. describe one of the smallest known Mesozoic avians, which indicates a clade-wide asynchronous pattern of osteogenesis and great variation in basal bird hatchling size and skeletal maturation tempo.

• Fabien Knoll
• Luis M. Chiappe
• Jose Luis Sanz

A diverse suite of pharmaceuticals contaminates stream and riparian food webs

Pharmaceuticals are widespread contaminants in surface waters. Here, Richmond and colleagues show that dozens of pharmaceuticals accumulate in  food chains of streams, including in predators in adjacent terrestrial ecosystems.

• Erinn K. Richmond
• Emma J. Rosi
• Michael R. Grace

An intrinsic association between olfactory identification and spatial memory in humans

Olfaction, the sense of smell, may have originally evolved to aid navigation in space, but there is no direct evidence of a link between olfaction and navigation in humans. Here the authors show that olfaction and spatial memory abilities are correlated and rely on similar brain regions in humans.

• Louisa Dahmani
• Raihaan M. Patel
• Véronique D. Bohbot

Systematic generation of biophysically detailed models for diverse cortical neuron types

Neocortical circuits exhibit diverse cell types that can be difficult to build into computational models. Here the authors employ a genetic algorithm-based parameter optimization to generate multi-compartment Hodgkin-Huxley models for diverse cell types in the Allen Cell Types Database.

• Nathan W. Gouwens
• Anton Arkhipov

Brain and psychological determinants of placebo pill response in chronic pain patients

People vary in the extent to which they feel better after taking an inert, placebo, treatment, but the basis for individual placebo response is unclear. Here, the authors show how brain structural and functional variables, as well as personality traits, predict placebo response in those with chronic back pain.

• Etienne Vachon-Presseau
• Sara E. Berger
• A. Vania Apkarian

Generalized leaky integrate-and-fire models classify multiple neuron types

Simplified neuron models, such as generalized leaky integrate-and-fire (GLIF) models, are extensively used in network modeling. Here the authors systematically generate and compare GLIF models of varying complexity for their ability to classify cell types in the Allen Cell Types Database and faithfully reproduce spike trains.

• Corinne Teeter
• Ramakrishnan Iyer
• Stefan Mihalas

Dietary stearic acid regulates mitochondria in vivo in humans

Dietary fatty acids have different effects on human health. Here, the authors show that ingestion of the fatty acid C18:0, but not of C16:0, rapidly leads to fusion of mitochondria and fatty acid oxidation in humans, possibly explaining the health benefits of C18:0.

• Deniz Senyilmaz-Tiebe
• Daniel H. Pfaff
• Aurelio A. Teleman

Engineering human pluripotent stem cells into a functional skeletal muscle tissue

The generation of functional skeletal muscle tissue from human pluripotent stem cells has not been reported. Here, the authors describe engineering of contractile skeletal muscle bundles in culture, which become vascularized and maintain functionality when transplanted into mice.

• Lingjun Rao
• Nenad Bursac

Topical ferumoxytol nanoparticles disrupt biofilms and prevent tooth decay in vivo via intrinsic catalytic activity

Ferumoxytol is a nanoparticle formulation approved for systemic use to treat iron deficiency. Liu et al. show that topical use of ferumoxytol, in combination with low concentrations of H 2 O 2 , disrupts intractable oral biofilms and prevents tooth decay in vitro and in an animal model.

• Pratap C. Naha

Honey bee Royalactin unlocks conserved pluripotency pathway in mammals

Royal jelly is the queen-maker for the honey bee that also has effects on longevity, fertility, and regeneration in mammals. Here the authors provide evidence that its major protein component Royalactin, and the mammalian structural analog Regina, maintain pluripotency in mouse ESCs by activating a ground-state pluripotency-like gene network.

• Derrick C. Wan
• Stefanie L. Morgan
• Kevin C. Wang

Deoxyribose and deoxysugar derivatives from photoprocessed astrophysical ice analogues and comparison to meteorites

Sugars are known to form from the UV photoprocessing of ices under astrophysical conditions. Here, the authors report the detection of deoxyribose, the sugar of DNA, and other deoxysugars from the UV photoprocessing of H 2 O:CH 3 OH ice mixtures, which are compared with materials from carbonaceous meteorites.

• Michel Nuevo
• George Cooper
• Scott A. Sandford

Genomic evidence of speciation reversal in ravens

Speciation reversal is known mainly from recently diverged lineages that have come into secondary contact following anthropogenic disturbance. Here, Kearns et al. use genomic and phylogenomic analyses to show that the Common Raven ( Corvus corax ) was formed by the ancient fusion of two non-sister lineages of ravens.

• Anna M. Kearns
• Marco Restani
• Kevin E. Omland

Analysis of 3800-year-old Yersinia pestis genomes suggests Bronze Age origin for bubonic plague

Yersinia pestis has caused infections (plague) in humans since the Early Bronze Age (5000 years ago). Here, Spyrou et al. reconstruct Y. pestis genomes from Late Bronze Age individuals, and find genomic evidence compatible with flea-mediated transmission causing bubonic plague.

• Maria A. Spyrou
• Rezeda I. Tukhbatova
• Johannes Krause

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