bioRxiv2017
It is presently unclear how much individual community members contribute to the overall metabolic output of a gut microbiota. To address this question, we used the honey bee, which harbors a relatively simple and remarkably conserved gut microbiota with striking parallels to the mammalian system and importance for bee health. Using untargeted metabolomics, we profiled metabolic changes in gnotobiotic bees that were colonized with the complete microbiota reconstituted from cultured strains. We then determined the contribution of individual community members in mono-colonized bees, and recapitulated our findings using in vitro cultures. Our results show that the honey bee gut microbiota utilizes a wide range of pollen-derived substrates including flavonoids and outer pollen wall components, suggesting a key role for degradation of recalcitrant secondary plant metabolites and pollen digestion. In turn, multiple species were responsible for the accumulation of organic acids and polyphenol degradation products, and a specific gut symbiont, Bifidobacterium asteroides, stimulated the production of host hormones known to impact bee development. While we found evidence for cross-feeding interactions, [~]80% of the identified metabolic changes were also observed in mono-colonized bees with Lactobacilli being responsible for the largest share of the metabolic output. These results suggest that bacteria in the honey bee gut colonize largely independent metabolic niches, which may be a general characteristic of gut microbiomes. Our study reveals diverse metabolic functions of gut bacteria that are likely to contribute to bee health, and provide fundamental insights into how metabolic functions are partitioned within gut communities.\n\nAuthor summaryHoney bees are important pollinators that harbor a simple gut microbiota with striking parallels to the mammalian system. This makes them relevant models to study gut microbiota functions and its impact on host health. We applied untargeted metabolomics to characterize metabolic changes induced by the gut microbiota, and to characterize contributions of the major community members. We find that the gut microbiota digests recalcitrant substrates derived from the bees pollen-diet. Most metabolic changes could be explained by the activity of individual community members suggesting substrate specificity and independent metabolic niches. Our study provides novel insights into the functional understanding of the bee gut microbiota and provides a framework for applying untargeted metabolomics to disentangle metabolic functions of gut bacteria.