Mosquito larvae continuously encounter microbes in their aquatic environment, which serve as food and play a critical role in successful development. In previous work, we isolated a Chromobacterium sp. (C.sp-P) with larvicidal activity from the midgut of dengue vector Aedes mosquitoes in Panama. In this study, we found a positive correlation between initial concentrations of C.sp-P and larval mortality rates, and that C.sp-P is more efficient at inducing larval mortality in a high nutrient environment. Multiple Chromobacterium species induce larval mortality with similar efficacy to C.sp-P except for C. subtsugae. We also found that a non-lethal dose of C.sp-P lengthens development time and increases mortality over multiple developmental stages, suggesting persistent effects of exposure. Additionally, we showed that larvicidal activity persists in the larval breeding water after removal of live bacteria, and that the larvicidal factor in C.sp-P-Treated water is smaller than 3 kDa, heat resistant to 90 °C, and lost after vacuum centrifugation. We showed that C.sp-P produces hydrogen cyanide in culture and in larval water at concentrations sufficient to kill An. gambiae larvae, and treatment of the larval water with a cyanide antidote eliminated larvicidal activity. We conclude that a potential mechanism by which C.sp-P can induce larval mortality is via production of hydrogen cyanide.
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