Integrated in vitro fermentation, transcriptomics and enzymatic property analyses uncover interaction between polysaccharide from the fruits of Lycium barbarum and Bacteroides ovatus

Abstract

Polysaccharides from the fruits of Lycium barbarum L. (LBPs) are the principal active constituents of L. barbarum, and it has been reported that LBPs exert regulatory effects on the gut microbiota, particularly in promoting the growth of Bacteroides. In this study, the in vitro anaerobic fermentation revealed that LBPs-4, a purified fraction of the crude LBPs, increased the relative abundances of 11 Bacteroides species, particularly B. ovatus. Results of the pure cultures indicated B. ovatus, B. thetaiotaomicron, B. fragilis and B. uniformis could effectively utilize LBPs-4 for their own growth. Transcriptome analysis of B. ovatus indicated that the degradation of LBPs-4 involved the up-regulation of three polysaccharide utilization loci (PULs). Among them, Bovatus_00022 in PUL1, which belongs to the GH28 family and is annotated as a polygalacturonase, is one of the major carbohydrate-active enzymes in the metabolism of LBPs-4. BOPG00022 was preliminarily confirmed to be effective in the degradation via the hydrolysis analysis. In conclusion, this study provided significant insights into the degradation mechanism of LBPs-4 employing gut microflora or enzymes as targets, providing a theoretical basis for the precise utilization and structural verification of complex glycans.