Garrett, E. | bioRxiv Science

bioRxiv2026

COSMOS: integrated vector-pathogen metagenomics for mosquito-borne disease

By 2050, almost half of the global population will be at risk of mosquito-borne disease. Effective response requires monitoring both pathogen transmission and vector abundance, yet these are typically assessed using separate assays with limited taxonomic breadth. Here we present COSMOS (COmprehensive Sequencing for MOSquito-borne disease), a targeted metagenomics workflow designed to reconstruct pathogen genomes and mosquito community composition directly from mixed field-collected samples. Over three annual rounds of a major Australian surveillance program, we evaluated >120,000 mosquitoes in 219 traps, with 98.7% agreement with surveillance data across seven monitored arboviruses, and additional detections of Sindbis virus and the state's first detection of encephalitic Little Sussex virus. Of 137 viral detections, 101 yielded near-complete genomes (>90% coverage) at median 95x depth. Using an accompanying computational workflow, COSMOS quantified mosquito composition, matching entomological estimates of reported vector species (CCC 0.78-0.89). Joint analysis of virus and vector composition identified structured mosquito communities associated with spatial and temporal environmental variation, allowing the ecological context of arbovirus detections to be characterised. Detections during the Murray Valley encephalitis virus outbreak in 2023 were concentrated within a narrowly defined mosquito-community space corresponding to rural communities dominated by the inland S-AUS sub-lineage of Culex annulirostris. Integrated vector-pathogen metagenomics provides ecological and evolutionary context for arbovirus activity within a single scalable workflow for surveillance and outbreak response.

microbiology↗

bioRxiv2019

Phase variation of a signal transduction system controls Clostridioides difficile colony morphology, motility, and virulence

Recent work has revealed that Clostridioides difficile, a major cause of nosocomial diarrheal disease, exhibits phenotypic heterogeneity within a clonal population as a result of phase variation. Many C. difficile strains representing multiple ribotypes develop two colony morphotypes, termed rough and smooth, but the biological implications of this phenomenon have not been explored. Here, we examine the molecular basis and physiological relevance of the distinct colony morphotypes produced by this bacterium. We show that C. difficile reversibly differentiates into rough and smooth colony morphologies, and that bacteria derived from the isolates display opposing surface and swimming motility behaviors. We identified an atypical phase-variable signal transduction system consisting of a histidine kinase and two response regulators, named herein CmrRST, which mediates the switch in colony morphology and motility behaviors. The CmrRST-regulated surface motility is independent of Type IV pili, suggesting a novel mechanism of surface expansion in C. difficile. Microscopic analysis of cell and colony structure indicates that CmrRST promotes the formation of elongated bacteria arranged in bundled chains, which may contribute to bacterial migration. In a hamster model of acute C. difficile disease, colony morphology correlates with virulence, and the CmrRST system is required for disease development. Furthermore, we provide evidence that CmrRST phase varies during infection, suggesting that the intestinal environment impacts the proportion of CmrRST-expressing C. difficile. Our findings indicate that C. difficile employs phase variation of the CmrRST signal transduction system to generate phenotypic heterogeneity during infection, with concomitant effects on bacterial physiology and pathogenesis.\n\nSignificance StatementPhenotypic heterogeneity within a genetically clonal population allows many mucosal pathogens to survive within their hosts, balancing the need to produce factors that promote colonization and persistence with the need to avoid the recognition of those factors by the host immune system. Recent work suggests that the human intestinal pathogen Clostridium difficile employs phase variation during infection to generate a heterogeneous population differing in swimming motility, toxin production, and more. This study identifies a signal transduction system that broadly impacts C. difficile physiology and behavior in vitro and in an animal model. Phase variation of this system is therefore poised to modulate the coordinated expression of multiple mechanisms influencing C. difficile disease development.

microbiology↗