Bacteria-mediated hypoxia functions as a signal for mosquito development

Abstract

Mosquitoes host communities of microbes in their digestive tract that consist primarily of bacteria. We previously reported that several mosquito species, including , do not develop beyond the first instar when fed a nutritionally complete diet in the absence of a gut microbiota. In contrast, several species of bacteria, including, rescue development of axenic larvae into adults. The molecular mechanisms underlying bacteria-dependent growth are unknown. Here, we designed a genetic screen around that identified high-affinity cytochrome oxidase as an essential bacterial gene product for mosquito growth. Bioassays showed that bacteria in nonsterile larvae and gnotobiotic larvae inoculated with wild-type reduced midgut oxygen levels below 5%, whereas larvae inoculated with mutants defective for cytochrome oxidase did not. Experiments further supported that hypoxia leads to growth and ecdysone-induced molting. Altogether, our results identify aerobic respiration by bacteria as a previously unknown but essential process for mosquito development.

Composition and functional roles of the gut microbiota in mosquitoes

“…Differences in bacterial species diversity have been reported between larval stadia of Culex quinquefasciatus [60]. Studies of Aedes aegypti further show that substantial numbers of bacteria in the gut die at the end of each instar prior to molting, which provides opportunity for altering gut community composition in the succeeding instar [61]. Other patterns of note include that bacterial species diversity is consistently higher in mosquito larvae than adults [13, 15, 18, 47], and that diversity is lower in laboratory reared versus field collected mosquitoes of the same species [13, 14, 35].…”

“…Functional assays supporting this hypothesis include the finding that gut hypoxia activates hypoxia-induced transcription factors (HIFs) in Ae. aegypti larvae which leads to activation of the insulin/insulin growth factor pathway, select mitogen activated kinases and other processes with essential growth functions [61, 70] (Figure 1). Transcriptome analysis also identifies several genes with functions in digestion and nutrient acquisition as additional targets that are potentially regulated by the gut microbiota or microbiota-induced hypoxia [71].…”

Bacterial microbiota assemblage in Aedes albopictus mosquitoes and its impacts on larval development

“…In Guangzhou, we designed three treatments: (a) water from natural flowerpots; (b) natural flowerpot water filtered by a 0.22-lm Millipore filter, which should have filtered >95% bacteria (Wang, Hammes, Boon, & Egli, 2007); and (c) ampicillin added to water from natural flowerpots, with a final antibiotic concentration of 100 lg/ ml. We used ampicillin as it is a wide-spectrum antibiotic and has been used in several studies on mosquito microbiota (Coon, Brown, & Strand, 2016;Coon et al, 2017). Fifty newly hatched larvae of the Ae.…”

Axenic Aedesaegyptidevelop without live bacteria, but exhibit delayed development and reduced oviposition

“…In this regard, there is some uncertainty as to whether these mosquitoes were truly axenic. In fact, a series of recent studies have reported that mosquitoes require a live bacterial symbiont for development 27,35,36 . Yet the studies describing the necessity of live bacteria generally ignored the role of microflora in supplying essential nutrients to the host.…”