Design of a synthetic consortium of human gut fibrolytic bacteria for the fermentation of bamboo fibers

The human gut microbiota plays a central role in the fermentation of dietary fibers, yet the contribution of defined bacterial communities to the utilization of structurally complex plant-derived substrates remains poorly understood. Here, we investigated the fermentation-associated metabolic activity of seven human gut bacterial strains cultivated individually or as defined three- and seven-member consortia in the presence of a commercial bamboo fiber substrate. Two bacterial consortia were assembled and compared to their constituent strains using bamboo fibers. Consortium cultures were characterized by distinct metabolite profiles including short-chain fatty acids, fermentation intermediates, reducing sugars, and gaseous metabolites. Consortium-level metabolite concentrations were further compared with the combined metabolic activities of the corresponding monocultures. Scanning electron microscopy revealed bacterial association with the fiber surface together with localized morphological alterations, including apparent perforations. Several metabolites deviated significantly from the arithmetic additive expectation in both the three- and seven-strain consortia, indicating non-additive metabolic behavior at the community level. Population analyses further showed marked changes in relative community composition, with a progressive predominance of Bacteroides species under the tested conditions. Together, these results show that defined bacterial communities exhibit distinct and non-additive metabolic behavior during incubation with commercial bamboo fiber. The observed community restructuring and bacterial association with the fiber surface are consistent with interactions among consortium members. These findings provide a basis for further investigation of the bacterial interactions involved in the microbial utilization of complex dietary fiber substrates.