Bacteria contribute to mosquito development via folate biosynthesis and energy storage

The mosquito microbiota impacts the physiology of its host and is essential for normal larval development, thereby influencing transmission of vector-borne pathogens. Germ-free mosquitoes generated with current methods show larval stunting and developmental deficits. Therefore, functional studies of the mosquito microbiota have so far mostly been limited to antibiotic treatments of emerging adults. In this study, we developed a novel approach to produce germ-free mosquitoes. It is based on reversible colonisation with bacteria genetically modified to allow complete decolonisation at the end of larval development. We show that, unlike germ-free mosquitoes previously produced using sterile diets, reversibly colonised mosquitoes show no developmental retardation and reach the same size as control adults. This uniquely allowed us to study the role of bacteria during larval development by inducing decolonisation at the beginning of the third larval instar. Based on a transcriptome analysis and diet supplementation experiments, we propose that bacteria support larval development by contributing to folate biosynthesis and by enhancing energy storage. Overall, this study provides a new tool to study the microbiota in insects and deepens our knowledge on the metabolic contribution of bacteria to mosquito development.