Effects of gut microbiota composition on vitellogenin expression in honeybees

Abstract

The relationship between animals and their gut microbiota is one of the most important symbiotic relationships in nature. The western honeybee, Apis mellifera, has received particular attention in microbiota research because of both its utility as a model organism and its economic importance. Honeybees have a specific gut microbiota which consists of few core members and contributes to the normal metabolism, immunity, behavior and endocrine signaling of the host. Among other genes, the honeybee microbiota affects the expression of vitellogenin, a multifunctional lipid-carrier protein that affects aging, immunity and behavior. The link between vitellogenin and the microbiota and the overlap between their functions suggest that vitellogenin could be the mediator of the microbiota effects on bee physiology. In this thesis, we explored how microbiota composition affects vitellogenin expression in honeybees, both locally and systemically. To do so, we used quantitative real-time PCR to study vitellogenin expression in the gut and fat body of honeybees experimentally inoculated with different members of the normal gut microbiota. Our results support the hypothesis that the various members of the microbiota contribute differently to the regulation of vitellogenin expression. We found that the gram-negative members of the honeybee microbiota, Snodograssella alvi and Gilliamella apicola, might be responsible for a systemic suppression of vitellogenin expression. We also found the gram-positive members of the microbiota to stimulate vitellogenin expression in the gut tissue, but we believe this might be an artifact of the experimental design. Nonetheless, the low efficiency of vitellogenin amplification and our inability to verify the presence and composition of the experimental microbiota in our bees reduce the quality of our data and prevent us from drawing any definitive conclusions.