Characterization and Immunomodulatory Activity of a Sulfated Polysaccharide from Natto-Derived Bacillus subtilis

Sulfated polysaccharides with significant biological activities were widely applied in functional food, cosmetic, biomedical and pharmaceutical industries. In this study, we established a practical high-throughput screening workflow for sulfated polysaccharide-producing bacteria and applied it to natto-derived isolates. Using this approach, a sulfated polysaccharide produced by Bacillus subtilis var. natto GX10-35 with the yield of 0.86 mg/mL was isolated and a purified polysaccharide fraction, GX10-35-P1, was obtained from its fermentation broth. Chemical analyses showed the sulfate content of the sulfated polysaccharide GX10-35-P1 was 12.02%. Spectroscopic analyses suggests that GX10-35-P1 is a sulfated exopolysaccharide with distinct structural features, with a proposed backbone consisting of α-D-Galp-(1→6)-α-D-Glcp-(1→→6)-α-D-Glcp-(1→→6)-α-D-Glcp-(1→6)-α-D-Galp3S-(1→6)-α-D-Glcp-(1→6)-α-D-Glcp-(1→6)-α-D-Glcp-(1→, indicating it could be classified as an unreported type of water-soluble sulfated exopolysaccharide from bacteria. Moreover, GX10-35-P1 could induce murine macrophage cells RAW264.7 to proliferation, phagocytic, release nitric oxide and promote the mRNA expression of TNF-α, IL-1β, IL-6 and IL-10 cytokines. These results indicate that GX10-35-P1 is a promising bacterial sulfated polysaccharide with potential for further investigation as an immunomodulatory agent.