Characterization of an EPS-producing bifidobacterial strain based on integration of phenotypic and complete genome sequencing data.

Bifidobacterium and Lactobacillus are known to be common members of the human intestinal microbiota, which plays important roles in maintaining the homeostasis of host gut microenvironment. Several bifidobacterial and lactobacilli strains have been used as probiotics for health benefits. The exopolysaccharides (EPS) produced by strains from Bifidobacterium and Lactobacillus are considered as beneficial traits mediating these beneficial effects. In this study, 21 strains belong to Bifidobacterium and Lactobacillus were isolated from healthy infants' stool and were screened for EPS-producing ability. Among these strains, B. longum XZM1 showed the highest EPS productivity, which was further confirmed and characterized. The complete genome of strain XZM1 was sequenced, which revealed the presence of a gene cluster for EPS-production. Furthermore, comparative genome analysis was performed among XZM1 and other strains from B. longum species. Following purification, the molecular weight of EPS from XZM1 was determined as 4023 Da (Mw) through gel permeation chromatography (GPC). Analysis of the EPS hydrolysates revealed that the EPS was composed of mannose, glucose, galactose, arabinose and fucose. Additionally, the EPS exhibited higher scavenging abilities toward hydroxyl than 1,1-diphenyl-2-picrylhydrazyl free radical (DPPH). Overall, these results suggest that XZM1 from B. longum species may be a promising probiotic candidate.