Properties of a variant of Streptococcus mutans altered in its ability to interact with glucans

After continuous subculture of Streptococcus mutans GS-5, the resultant organism, GS-5var, was found to be altered in its ability to undergo dextran- and sucrose-induced cell agglutination and to adhere to smooth surfaces in the presence of sucrose. Both GS-5 and GS-5var cells possessed the serotype c polysaccharide antigen, displayed similar growth kinetics, appeared to have similar metabolic and biosynthetic capabilities, and produced similar amounts of cell-associated and extracellular glucosyltransferase activity in chemically defined medium. GS-5 cells which had bound exogenous glucosyltransferase enzymes from either cell type were able to undergo sucrose-dependent adherence to smooth surfaces, whereas GS-5var cells which had bound comparable levels of glucosyltransferase activity were unable to adhere. In contrast to GS-5var cells, GS-5 cells were also able to adhere to preformed glucan deposits. In addition, [(14)C]glucan binding studies demonstrated that GS-5 cells were able to bind fourfold-greater levels of [(14)C]glucan relative to GS-5var cells having similar cell-associated glucosyltransferase activity. Further study of GS-5 cells also suggested the existence of a glucan binding site, distinct from the cell-associated glucosyltransferase activity, which is important in dextran-induced agglutination and sucrose-dependent adherence to smooth surfaces. These results are discussed in terms of the alteration of the GS-5var cells and their possible relationship to the putative receptors for glucosyltransferase enzymes and glucans on the cell surface of S. mutans.