STRUCTURE OF AN EXOCELLULAR POLYSACCHARIDE PRODUCED BY STREPTOCOCCUS-THERMOPHILUS

Streptococcus thermophilus strains grown on skimmed milk produced a viscosifying, exocellular, and water-soluble polysaccharide which contains d-glucose, d-galactose, and N-acetyl-d-galactosamine in the ratio of 1:2:1. Methylation analysis identified the glycosidic linkages in the tetrasaccharidic repeating-unit, and Smith degradation and nitrous deamination after N-deacetylation gave the sequence of monosaccharides in the repeating-unit. The anomeric configurations of the sugar residues were determined by oxidation of the peracetylated polysaccharide with chromium trioxide and by 1H- and 13C-n.m.r. spectroscopy. The following structure was assigned to the repeating unit of the polysaccharide, →3)-β-d-Galp-(1→3)-[α-d-Galp-(1→6)]-β-d-Glcp-(1→3)-α-d-GalpNAc-(1→. © 1990.