Effects of Entomopathogenic Chromobacterium (Csp_P) Exposure on the Microbiota and Fitness of Anopheles gambiae
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Date
2016-04-20
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Johns Hopkins University
Abstract
Evidence that the mosquito’s microbiota can alter Plasmodium susceptibility has led to interest in manipulating the mosquito microbiome to interfere with malaria transmission. Microbes that mosquitoes naturally harbor may modulate vectorial capacity by altering vector competence, daily survival, blood-feeding behavior or vector density. Anopheles exposed to Chromobacterium (Csp_P), a bacterium isolated from field-caught Aedes aegypti, are more resistant to Plasmodium infection and are killed efficiently. This study evaluated the impact of Csp_P on fitness, multigenerational killing efficiency, and midgut microbiota composition in exposed Anopheles gambiae. To assess the effects on fitness parameters in exposed females, mosquitoes were fed a low (10^2 CFU/mL) or a high (10^7 CFU/mL) dose of Csp_P or Pantoea spp. (P. sp.) in an artificial nectar meal, and were subsequently offered a blood meal and allowed to oviposit. In a separate experiment, the offspring of females fed Csp_P (10^7 CFU/mL) were reared to measure transgenerational fitness effects. First generation offspring were exposed to Csp_P as either larvae or adults to test Csp_P’s multigenerational killing capacity. To measure the effect of Csp_P ingestion on the cultivable midgut microbiota, females were fed a high dose of either Csp_P, Enterobacter sp. Zambia (Esp_Z), or P sp., and, at 24 and 96 hours, individual midguts were dissected and plated on LB agar. Exposure to either dose of Csp_P or P. sp. did not alter the proportion ovipositing females or the number of eggs oviposited. Only adults fed Csp_P at the higher dose experienced reduced longevity. Maternal exposure to Csp_P significantly decreased survival, time to pupation, and survival of larval offspring; however, the life span and sex ratio of adult offspring was unaffected. When challenged with Csp_P, the F1 offspring of Csp_P-exposed females were killed as quickly as the F1 larvae of PBS-controls. Ingestion of Csp_P does not affect the total number or prevalence of the endogenous, cultivable bacteria. Overall, Csp_P (10^7 CFU/mL) attenuates the lifespan of exposed females without significantly impacting fecundity, oviposition, or midgut microbiota composition. Furthermore, this bacterial strain perturbs the development and eclosion of first-generation offspring and maintains killing efficiency over at least two consecutive generations.
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Keywords
Chromobacterium, Anopheles gambiae, Malaria