Differential carbohydrate utilization and organic acid production by honey bee symbionts

The honey bee worker gut is host to a community of bacteria that primarily comprises 8-10 bacterial species. Collectively, these microbes break down and ferment saccharides present in the host’s diet. The model of metabolism for these gut symbionts is rooted in previous analyses of genomes, metagenomes, and metatranscriptomes of this environment. Importantly, there is a correlation between the composition of the gut microbiome and weight gain in the honey bee, suggesting that bacterial production of organic acids might contribute to the observed phenomenon. Here we identify potential metabolic contributions of symbionts within the honey bee gut. We show significant variation in the metabolic capabilities of these microbes, highlighting the fact that although the microbiota appears simple and consistent based on 16S rRNA gene profiling, strains are highly variable in their ability to use specific carbohydrates and produce organic acids. Finally, we confirm that the honey bee core microbes, especially a clade of γ-proteobacteria (i.e. Gilliamella ), are highly active in vivo , expressing key enzymatic genes critical for utilizing plant-derived molecules and producing organic acids. These results suggest that Gilliamella , and other core taxa, may contribute significantly to weight gain in the honey bee, specifically through the production of organic acids.