Structural characterization of the immunostimulatory exopolysaccharide produced by Leuconostoc mesenteroides strain NTM048.

The exopolysaccharide (EPS) produced by probiotic Leuconostoc mesenteroides subsp. mesenteroides strain NTM048 has been reported to be an immunostimulant that enhances mucosal IgA production. In this study, we found that intranasal administration of mice with the EPS and an antigen (ovalbumin) resulted in secretion of antigen-specific IgA and IgG in the airway mucosa and the serum, suggesting that the EPS has the adjuvant activity for use with mucosal vaccination. Methylation analysis coupled to GC-MS, and 1D and 2D NMR spectroscopy revealed that 94% of the EPS consists of an α-(1 → 6) glucan containing 4% of 1→3-linked α-glucose branches. To determine structures of minor components, we enzymatically digested the glucan with dextranase and used 2D NMR spectroscopy to identify the remaining polymer as a fructan (or fructans), containing both β-(2 → 6)- and β-(2 → 1)-linked fructofuranose residues. These residues may either enter into separate polymers of each linkage type or form a mixed fructan containing both linkage types.