Regulation of Glucosyl- and Fructosyltransferase Synthesis by Continuous Cultures of Streptococcus mutans

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Abstract
S. mutans strain Ingbritt and its derivative B7, which were passaged through monkeys, were used to investigate how the synthesis of extracellular glucosyl- and fructosyltransferases is regulated. The most active enzyme from C-limited continuous cultures was a fructosyltransferase; enzymes catalyzing the formation of water-insoluble glucans from sucrose were relatively inactive. Dextran sucrase (EC 2.4.1.5), which catalyzes soluble glucan synthesis, was most active in the supernatant fluid from cultures grown with excess glucose, fructose or sucrose, but full activity was detected only when the enzyme was incubated with both sucrose and dextran. Little dextransucrase activity was detected in C-limited cultures. Glucosyl- and fructosyltransferases are constitutive enzymes in that they are synthesized at similar rates during growth with an excess of the substrate or of the products of the reactions which they catalyze. Although the Ingbritt strain was originally isolated from a carious lesion, it is now a poor source of glucosyltransferase activity. Glucosyltransferases were extremely active in cultures of a recent clinical isolate, strain 3209, and were apparently induced during growth with excess glucose.