In Vitro Cholesterol-Lowering Bioactivity, Synthetic Pathway, and Structural Characterization of Exopolysaccharide Synthesized by <i>Schleiferilactobacillus harbinensis</i> Z171

A strain identified as <i>Schleiferilactobacillus harbinensis</i> was isolated from Chinese sauerkraut, and its exopolysaccharide (EPS) exhibited excellent in vitro cholesterol-lowering bioactivity. Besides, the whole genome of this strain and the structure characteristics of the purified EPS were investigated in this study. <i>S. harbinensis</i> Z171 presented a strong EPS production capacity, with five nucleotide sugar biosynthesis pathways regulated by an EPS synthesis gene cluster. Structural characterization revealed that the purified fraction F-EPS1A was a neutral polysaccharide with a molecular weight of 6.4 × 10⁴ Da. The structure of F-EPS1A contained a backbone that comprised blocks of four 1,2-linked and three 1,3-linked alpha mannose units. Some 1,2-linked alpha mannose residues were branched at C6 with side chains formed by single alpha mannose or a disaccharide consisting of 1,6-linked alpha mannose residues. The structural characteristics endowed F-EPS1A with a high level of cholesterol-lowering bioactivity. In addition, whole genome analysis indicated that <i>S. harbinensis</i> Z171 possessed a strong EPS production capacity. These findings suggested that the EPS produced by <i>S. harbinensis</i> Z171 could be applied as a potential cholesterol-lowering prebiotic agent or supplement in functional food.