Effect of sucrose in culture media on the location of glucosyltransferase of Streptococcus mutans and cell adherence to glass surfaces

Abstract

Streptococcus mutans strain B13 (serotype D) almost exclusively produced free glucosyltransferase (GTase) in the culture supernatant when grown in sucrose-free TTY broth medium, which was composed of Trypticase (Baltimore Biological Laboratory [BBL] Cockeysville, Md.), tryptose (Difco Laboratories, Detroit, Mich.), yeast extract (BBL), salts, and 1% glucose. Organisms grown in sucrose-free TTY broth retained very weak cell-associated GTase activity and did not adhere significantly to glass surfaces in the presence of exogenous sucrose. If sucrose was added to TTY broth, however, GTase was found on the cell surface where cell-bound, water-insoluble glucans were synthesized. Most commercially available products of Todd-Hewitt broth were found to contain trace amounts of sucrose, as did Trypticase soy broth (BBL), whereas brain heart infusion broth (Difco and BBL) was found to be essentially free of sucrose. Almost all detectable GTase activity was cell associated when S. mutans B13 was grown in Todd-Hewitt or trypticase soy broth. Heat-treated B13 cells grown in Todd-Hewitt broth and cell-free, water-insoluble glucans bound free GTase and produced marked adherence in the presence of sucrose. Experiments strongly suggest that the binding sites for free GTase are the surface glucans, and cell-associated and extracellular GTases are most likely alternate states of the same enzyme protein.