Colwell, R. | Search bioRxiv

bioRxiv2017

Spores and soil from six sides: interdisciplinarity and the environmental biology of anthrax (Bacillus anthracis)

Environmentally Transmitted Diseases Are Comparatively Poorly Understood And Managed, And Their Ecology Is Particularly Understudied. Here We Identify Challenges Of Studying Environmental Transmission And Persistence With A Six-Sided Interdisciplinary Review Of The Biology Of Anthrax (Bacillus Anthracis). Anthrax Is A Zoonotic Disease Capable Of Maintaining Infectious Spore Banks In Soil For Decades (Or Even Potentially Centuries), And The Mechanisms Of Its Environmental Persistence Have Been The Topic Of Significant Research And Controversy. Where Anthrax Is Endemic, It Plays An Important Ecological Role, Shaping The Dynamics Of Entire Herbivore Communities. The Complex Eco-Epidemiology Of Anthrax, And The Mysterious Biology Of Bacillus Anthracis During Its Environmental Stage, Have Necessitated An Interdisciplinary Approach To Pathogen Research. Here, We Illustrate Different Disciplinary Perspectives Through Key Advances Made By Researchers Working In Etosha National Park, A Long-Term Ecological Research Site In Namibia That Has Exemplified The Complexities Of AnthraxS Enzootic Process Over Decades Of Surveillance. In Etosha, The Role Of Scavengers And Alternate Routes (Waterborne Transmission And Flies) Has Proved Unimportant, Relative To The Long-Term Persistence Of Anthrax Spores In Soil And Their Infection Of Herbivore Hosts. Carcass Deposition Facilitates Green-Ups Of Vegetation To Attract Herbivores, Potentially Facilitated By Anthrax Spores Role In The Rhizosphere. The Underlying Seasonal Pattern Of Vegetation, And Herbivores Immune And Behavioral Responses To Anthrax Risk, Interact To Produce Regular \"Anthrax Seasons\" That Appear To Be A Stable Feature Of The Etosha Ecosystem. Through The Lens Of Microbiologists, Geneticists, Immunologists, Ecologists, Epidemiologists, And Clinicians, We Discuss How Anthrax Dynamics Are Shaped At The Smallest Scale By Population Genetics And Interactions Within The Bacterial Communities Up To The Broadest Scales Of Ecosystem Structure. We Illustrate The Benefits And Challenges Of This Interdisciplinary Approach To Disease Ecology, And Suggest Ways Anthrax Might Offer Insights Into The Biology Of Other Important Pathogens. Bacillus Anthracis, And The More Recently Emerged Bacillus Cereus Biovar Anthracis, Share Key Features With Other Environmentally-Transmitted Pathogens, Including Several Zoonoses And Panzootics Of Special Interest For Global Health And Conservation Efforts. Understanding The Dynamics Of Anthrax, And Developing Interdisciplinary Research Programs That Explore Environmental Persistence, Is A Critical Step Forward For Understanding These Emerging Threats.

ecology↗

bioRxiv2017

Comprehensive Benchmarking and Ensemble Approaches for Metagenomic Classifiers

BackgroundOne of the main challenges in metagenomics is the identification of microorganisms in clinical and environmental samples. While an extensive and heterogeneous set of computational tools is available to classify microorganisms using whole genome shotgun sequencing data, comprehensive comparisons of these methods are limited. In this study, we use the largest (n=35) to date set of laboratory-generated and simulated controls across 846 species to evaluate the performance of eleven metagenomics classifiers. We also assess the effects of filtering and combining tools to reduce the number of false positives.\n\nResultsTools were characterized on the basis of their ability to (1) identify taxa at the genus, species, and strain levels, (2) quantify relative abundance measures of taxa, and (3) classify individual reads to the species level. Strikingly, the number of species identified by the eleven tools can differ by over three orders of magnitude on the same datasets. However, various strategies can ameliorate taxonomic misclassification, including abundance filtering, ensemble approaches, and tool intersection. Indeed, leveraging tools with different heuristics is beneficial for improved precision. Nevertheless, these strategies were often insufficient to completely eliminate false positives from environmental samples, which are especially important where they concern medically relevant species and where customized tools may be required.\n\nConclusionsThe results of this study provide positive controls, titrated standards, and a guide for selecting tools for metagenomic analyses by comparing ranges of precision and recall. We show that proper experimental design and analysis parameters, including depth of sequencing, choice of classifier or classifiers, database size, and filtering, can reduce false positives, provide greater resolution of species in complex metagenomic samples, and improve the interpretation of results.

genomics↗