The claim of primacy of human gut Bacteroides ovatus in dietary cellobiose degradation

A demonstration of cellulose degrading bacterium from human gut changed our view that human cannot degrade the cellulose. However, investigation of cellulose degradation by human gut microbiota on molecular level has not been completed so far. We showed here, using cellobiose as a model that promoted the growth of human gut key members, such as Bacteroides ovatus (BO), to clarify the molecular mechanism. Our results showed that a new polysaccharide utilization locus (PUL) from BO was involved in the cellobiose capturing and degradation. Further, two new cellulases BACOVA_02626(GH5) and BACOVA_02630(GH5) on the cell surface performed the degradation of cellobiose into glucose were determined. The predicted structures of BACOVA_02626(GH5) and BACOVA_02630(GH5) were highly homologous with the cellulase from soil bacteria, and the catalytic residues were highly conservative with two glutamate residues. In murine experiment, we observed cellobiose reshaped the composition of gut microbiota and probably modified the metabolic function of bacteria. Taken together, our findings further highlight the evidence of cellulose can be degraded by human gut microbes and provide new insight in the field of investigation on cellulose.

Automated summary

A demonstration of cellulose degrading bacterium from human gut challenged the belief that humans cannot degrade cellulose. However, research on the molecular level of cellulose degradation by human gut microbiota is still incomplete. Using cellobiose as a model, we investigated the molecular mechanism behind cellulose degradation by key members of the human gut microbiota, such as Bacteroides ovatus (BO). Our results showed that a new polysaccharide utilization locus (PUL) from BO was involved in cellobiose capturing and degradation, and two new cellulases on the cell surface, BACOVA_02626 (GH5) and BACOVA_02630 (GH5), were responsible for cellobiose degradation into glucose. Studies on mice also revealed that cellobiose reshaped the gut microbiota composition and potentially modified bacterial metabolic functions. These findings provide further evidence of cellulose degradation by human gut microbes and contribute new insights to cellulose research.