Ecological Importance of Cross-Feeding of the Intermediate Metabolite 1,2-Propanediol between Bacterial Gut Symbionts.

Cross-feeding based on the metabolite 1,2-propanediol has been proposed to have an important role in the establishment of trophic interactions among gut symbionts, but its ecological importance has not been empirically established. Here, we show that growth of (syn. ) ATCC PTA 6475 is enhanced through 1,2-propanediol produced by UCC2003 and MG1655 from the metabolization of fucose and rhamnose, respectively. Work with isogenic mutants showed that the trophic interaction is dependent on the operon in , which encodes the ability to use 1,2-propanediol, and the l-fucose permease () gene in , which is required for 1,2-propanediol formation from fucose. Experiments in gnotobiotic mice revealed that, although the operon bestows a fitness burden on ATCC PTA 6475 in the mouse digestive tract, the ecological performance of the strain was enhanced in the presence of UCC2003 and the mucus-degrading species The use of the respective and mutants of and in the mouse experiments indicated that the trophic interaction was specifically based on 1,2-propanediol. Overall, our work established the ecological importance of cross-feeding relationships based on 1,2-propanediol for the fitness of a bacterial symbiont in the vertebrate gut. Through experiments in gnotobiotic mice that employed isogenic mutants of bacterial strains that produce () and utilize () 1,2-propanediol, this study provides mechanistic insight into the ecological ramifications of a trophic interaction between gut symbionts. The findings improve our understanding on how cross-feeding influences the competitive fitness of in the vertebrate gut and revealed a putative selective force that shaped the evolution of the species. The findings are relevant since they provide a basis to design rational microbial-based strategies to modulate gut ecosystems, which could employ mixtures of bacterial strains that establish trophic interactions or a personalized approach based on the ability of a resident microbiota to provide resources for the incoming microbe.