A Gut Commensal Bacterium Promotes Mosquito Permissiveness to Arboviruses

Mosquitoes are hematophagous vectors that can acquire human viruses in their intestinal tract. Here, we define a mosquito gut commensal bacterium that promotes permissiveness to arboviruses. Antibiotic depletion of gut bacteria impaired arboviral infection of a lab-adapted Aedes aegypti mosquito strain. Reconstitution of individual cultivable gut bacteria in antibiotic-treated mosquitoes identified Serratia marcescens as a commensal bacterium critical for efficient arboviral acquisition. S. marcescens facilitates arboviral infection through a secreted protein named SmEnhancin, which digests membrane-bound mucins on the mosquito gut epithelia, thereby enhancing viral dissemination. Field Aedes mosquitoes positive for S. marcescens were more permissive to dengue virus infection than those free of S. marcescens. Oral introduction of S. marcescens into field mosquitoes that lack this bacterium rendered these mosquitoes highly susceptible to arboviruses. This study defines a commensal-driven mechanism that contributes to vector competence, and extends our understanding of multipartite interactions among hosts, the gut microbiome, and viruses.