Both living bacteria and eukaryotes in the mosquito gut promote growth of larvae

Abstract

We recently reported that larval stage Aedes aegypti and several other species of mosquitoes grow when living bacteria are present in the gut but do not grow when living bacteria are absent. We further reported that living bacteria induce a hypoxia signal in the gut, which activates hypoxia-induced transcription factors and other processes larvae require for growth. In this study we assessed whether other types of organisms induce mosquito larvae to grow and asked if the density of non-living microbes or diet larvae are fed obviate the requirement for living organisms prior results indicated are required for growth. Using culture conditions identical to our own prior studies, we determined that inoculation density of living Escherichia coli positively affected growth rates of Ae. aegypti larvae, whereas non-living E. coli had no effect on growth across the same range of inoculation densities. A living yeast, alga, and insect cell line induced axenic Ae. aegypti first instars to grow, and stimulated similar levels of midgut hypoxia, HIF-α stabilization, and neutral lipid accumulation in the fat body as E. coli. However, the same organisms had no effect on larval growth if heat-killed. In addition, no axenic larvae molted when fed two other diets, when fed diets supplemented with heat-killed microbes or lysed and heat-killed microbes. Experiments conducted with An. gambiae yielded similar findings. Taken together, our results indicate that organisms from different prokaryotic and eukaryotic groups induce mosquito larvae to grow, whereas no conditions were identified that stimulated larvae to grow in the absence of living organisms.

Composition and functional roles of the gut microbiota in mosquitoes

“…gambiae larvae grow beyond the first instar but did find that several eukaryotic gut community members induce gut hypoxia, HIF signaling and larval growth if viable [73]. However, the preceding study and others also show that the proportion of larvae that develop into adults as well as the size, longevity, and fecundity of surviving adults varies among different bacteria and unicellular eukaryotes [18, 42,73–75]. Thus, microbes from diverse taxa can induce a gut hypoxia response and larval growth, whereas in the absence of micriobiota larvae do not grow or molt.…”

CRISPR/Cas9-mediated gene deletion of the ompA gene in symbiotic Enterobacter impairs biofilm formation and reduces gut colonization of Aedes aegypti mosquitoes

“…aegypti whereby an ompA mutant of E. coli did not influence growth reared in a mono-association [69]. Using a similar gnotobiotic system that exploits the ability to sterilize mosquito eggs and rescue development by nutritional supplementation, several recent reports describe approaches to create bacteria-free mosquitoes [69, 70]. Here, we reared mosquitoes in a mono-association where they were only subjected to Enterobacter.…”

Impact of Gut Bacteria on the Infection and Transmission of Pathogenic Arboviruses by Biting Midges and Mosquitoes

“…The online version of this article (https://doi.org/10.1007/s00248-020-01517-6) contains supplementary material, which is available to authorized users. reduced in mosquitoes reared free of living bacteria [5,6]. Of particular interest is the tripartite interaction among the insect vector, their midgut bacteria, and the pathogens that these vectors may transmit [7,8].…”