Structural characterization of exopolysaccharides from biofilm of a cariogenic streptococci

Soluble (EPS-SOL), as well as insoluble extracellular polysaccharide (EPS-INSOL), extracted from biofilm of Streptococcus mutans, were analyzed by nuclear magnetic resonance spectroscopy, methylation analysis, and a controlled Smith degradation. EPS-SOL was a branched α-glucan containing a (1 → 6)-and (1 → 3)-linkages. EPS-INSOL was a branched α-glucan with similar linkages, but with a (1 → 3)-linked main-chain partially substituted at O-6 with Glcp-(1 → 6)-Glcp-side chains. Biofilm EPS had a distinct chemical structure compared with those synthesized by plankton cells or by purified enzymes from S. mutans, which could indicate different mechanisms for its degradation.