Structural investigation of an extracellular polysaccharide produced by the cariogenic bacterium Streptococcus mutans strain UA159

The structure of an extracellular polysaccharide EPS159 produced from sucrose by Streptococcus mutans UA159 was investigated through the main oligosaccharides obtained from partial acid hydrolysis, monosaccharide/methylation analysis, and 1D/2D 1H NMR spectroscopy. The results showed that EPS159 contained terminal, 3-substituted, 6-substituted, and 3,6-disubstituted α-d-glucopyranose residues in a molar percentage of 14, 18, 54, and 14%. The backbone of EPS159 was composed of →6)Glcp(1→ residues, and about 20% of the →6)Glcp(1→ residues was substituted at 3-OH by →3)Glcp(1→ and/or Glcp(1→ residues to form side chains. A composite model of EPS159, that includes all identified structural features, was formulated: