Metabolism of the Polysaccharides of Human Dental Plaque: Release of Dextranase in Batch Cultures of Streptococcus mutans

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Abstract
Dextranase activity was determined in cell extracts and cell-free filtrates of S. mutans strains which had been grown in batch culture. Exodextranase activity was located chiefly in cell extracts; endodextranase was mainly extracellular. Release of endodextranase began early in the exponential phase of growth, and ended when the concentration of residual sugar was low. Thus, dextranase expression was associated with rapidly growing cells and the yield of dextranase was increased severalfold when the initial concentration of D-glucose in the medium was changed from 0.5% to 2%. The endodextranase was not stable at pH 5; control of the pH of the culture was essential to preserve active dextranase during overnight growth. Strain Ingbritt (serotype c) and serotype d strains were the best dextranase producers; other strains (serotypes a, b, c, e and f) displayed much lower activity. The ability to produce endodextranase and to synthesize .alpha.-D-glucans with a high proportion of (1 .fwdarw. 3)-linked sequences, appeared to be related properties. The release of 2 enzymes, namely endodextranase and the D-glucosyltransferase (GTF-I) that synthesizes (1 .fwdarw. 3)-.alpha.-D-glucan, are possibly factors that contribute to the cariogenicity of S. mutans serotype d.
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