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

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Abstract
S. mutans strain B13 (serotype d) almost exclusively produced free glucosyltransferase [EC 2.4.1.5] (GTase) in the culture supernatant when grown in sucrose-free TTY broth medium, which was composed of Trypticase, tryptose, 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, GTase was found on the cell surface where cell-bound, water-insoluble glucans were synthesized. Most commercially available products of Todd-Hewitt broth contained trace amounts of sucrose, as did Trypticase soy broth (BBL), but brain heart infusion broth was essentially free of sucrose. Almost all detectable GTase activity was cell associated when S. mutans B3 was grown in Todd-Hewitt or trypticase soy broth. Heat-treated B3 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.