We coupled microbiome manipulations with RNA-sequencing of brain and gut tissues, cuticular hydrocarbon (CHC) profiling by GC-MS, and automated behavioural tracking to unravel the host responses to microbial colonization along the honey bee gut-brain axis. To gain a better understanding of the brain regions involved in the putative interactions between the gut microbiota and the host nervous system, we dissected the brains into three macro-regions that are responsible for learning and memory, perception of olfactory and gustatory stimuli, and visual processing, respectively. We verified that microbial manipulations were successful by 16S rRNA gene amplicon sequencing and qPCR with universal bacterial primers, assessing both the composition and total load of the gut community in gut tissues.
The analyses of these large RNA-sequencing (involving 160 samples) and CHC datasets demonstrated for the first time that the gut bacterial community affects the physiology of the brain in a eusocial animal, without changing the CHC profiles that social insects use to recognize their nestmates and project their fertility status. Our results produced a short list of candidates for further functional studies into the proximate mechanisms of host-brain-symbiont interactions. They also highlighted that the brain region most affected by the gut microbiota was the one involved in the perception of olfactory and gustatory stimuli. The candidate genes include several with known involvement in brain development in other organisms, and the functional categories to which they belong show some overlap with those associated with the gut microbiota – brain axis of vertebrate models. We further developed an automated behavioural tracking approach to investigate the social behavioural phenotypes of the bees while keeping them in a microbiota-depleted state, which allowed us to assess the effects of the gut microbiota on the honey bee social network structure. These large datasets have been successfully collected, and the analyses are ongoing and will be finalized in the next few months.
As part of this project, a review on the gut microbiota – brain axis of insects was published in Current Opinion in Insect Science.
