The characterization of the midgut microbiota in lab-reared mosquitoes and the role of dopachrome conversion enzyme in mosquito melanization response -

Abstract

The gut microbiota in insects controls several aspects of the host physiology as well as vector competence in mosquito vectors of disease. The knowledge of the different factors that converge to control the structure of the gut microbiota in insects remains rudimentary. In the first part of this thesis project, we follow the dynamics of the midgut microbiome in two mosquito species, Anopheles gambiae and Aedes albopictus, reared in a stable physico-chemical environment in the insectary and given the same food over a period of seven generations. Results showed that despite sharing the same environment, female mosquitoes from the two species differed significantly with respect to their gut microbiota composition. Interestingly, significant differences were also observed between individuals of the same species over several generations and even within the same generation. Co-culturing both species in the same larval pans also resulted in significant differences in their microbiota structure suggesting that the species-specific differences influence the dynamics of the microbiome composition in the mosquito midgut. This was evident for the two major OTUs, Elizabethkingia and Enterobacter, which showed significant differences in their loads between the two different species even though they shared the same ecological niche. In conclusion, our results show that the gut microbiota of mosquitoes passes through highly dynamic phases even when reared in a relatively controlled physico-chemical environment. In the second part of this project, we investigated the contribution of dopachrome conversion enzyme (DCE) to the process of melanogenesis during microbial infections. The melanization reaction is an important immune response in mosquitoes. Melanin synthesis can proceed through two independent branches, one requiring DCE and the second dopachrome decarboxylase (DDC). Here, we show that silencing DCE leads to a significant reduction in the number of melanized P. berghei ookinetes in refractory mosquitoes silenced for C