Differences in utilization and metabolism of Ulva lactuca polysaccharide by human gut Bacteroides species in the in vitro fermentation

Abstract

Ulva lactuca polysaccharide (ULP), a sulfated polysaccharide, has been widely used in Asia. However, its digestion process and utilization by gut microbiota remain poorly understood. In this study, the in vitro simulated digestion and fermentation were used to analyze the digestibility of ULP. The results showed that ULP was not degraded during simulated digestion, but was utilized by human fecal microbiota. 16S rRNA sequencing revealed that ULP significantly increased the abundance of Bacteroides. Further evaluation of seven Bacteroides species showed that only B. thetaiotaomicron and B. vulgatus could utilize ULP. Interestingly, these two species exhibited different utilization patterns. B. vulgatus preferentially utilized rhamnose of ULP over glucuronic acid to promote growth. Metabolite profiles of B. thetaiotaomicron and B. vulgatus during in vitro fermentation with ULP as the sole carbon source were different. Although both B. thetaiotaomicron and B. vulgatus utilized ULP to produce various metabolites such as acetic acid, propionic acid, cysteic acid and riboflavin, B. thetaiotaomicron accumulated metabolites, such as linoleic acid, that were not accumulated by B. vulgatus. The effects of ULP on the metabolic pathways of B. thetaiotaomicron and B. vulgatus differed. These findings provide a new perspective on the utilization of ULP by human gut microbiota.

Keywords: Bacteroides; Digestion; Ulva lactuca polysaccharides.