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

Abstract

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.

Keywords: Human gut microbiota; bacteroide ovatus; cellobiose; cellulase; structure.

Figure 1.

Growth curves of HGM grown on cello-oligosaccharides were detected.

Figure 2.

The degradation products of cellobiose were analyzed by TLC.

Figure 3.

Polysaccharide utilization loci (PULs) were screened by RNA-seq and confirmed by RT-qPCR.

Figure 4.

Two new cellulases were determined.

Figure 5.

Structure biology of BACOVA_02626^GH5 and BACOVA_02630^GH5.

Figure 6.

Function of cellobiose on the composition of gut microbiota was analyzed by diversity sequencing based on 16S rRNA.

Figure 7.

Predication of metabolic function of bacteria and inflammatory factors detection.

Figure 8.

Model of degradation of cellobiose by human gut BO. Two new cellulases on the cell surface conferred the degradation of cellobiose into glucose were determined. In vivo test, we observed that cellobiose reshaped the composition of gut microbiota, and the abundance of LR and BO were enriched significantly after eight weeks administration by gavage.