A Gut Symbiotic Bacterium Renders Mosquito Resistance to Infection Through Activation of Mosquito Immune Responses.

The malaria development in the mosquito midgut is a complex process that results in considerable parasite losses. The mosquito gut microbiota influences the outcome of pathogen infection in mosquitoes, but the underlying mechanisms through which gut symbiotic bacteria affect vector competence remain elusive. Here, we identified two strains (Y1 and J1) isolated from field-caught female from China and assessed their effect on development in . Colonization of midgut by Y1 significantly renders the mosquito resistant to infection, while J1 has no impact on parasite development. Parasite inhibition by Y1 is induced by the activation of the mosquito immune system. Genome-wide transcriptomic analysis by RNA-seq shows a similar pattern of midgut gene expression in response to Y1 and J1 in sugar-fed mosquitoes. However, 24 h after blood ingestion Y1 modulates more midgut genes than J1 including the c-type lectins (CTLs), CLIP serine proteases and other immune effectors. Furthermore, silencing of several Y1-induced anti- factors like the thioester-containing protein 1 (TEP1), fibrinogen immunolectin 9 (FBN9) or leucine-rich repeat protein LRRD7 can rescue parasite oocyst development in the presence of Y1, suggesting that these factors modulate the Y1-mediated anti- effect. This study enhances our understanding of how gut bacteria influence mosquito- interactions.