Regulation and extracellular glucosyltransferase production and the relationship between extracellular and cell-associated activities in Streptococcus mutans

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Abstract
The regulation of extracellular glucosyltransferase [EC 2.3.1.5] production in S. mutans GS-5 was studied using a chemically defined medium. Most of the glucosyltransferase activity produced by cells grown in the chemically defined medium was extracellular, in contrast with the distribution between cell-associated and extracellular glucosyltransferase activity when cells were grown in complex medium. The production of extracellular glucosyltransferase activity coincided with the logarithmic growth phase, and further accumulation ceased when glucose was exhausted from the medium. Accumulation of extracellular glucosyltransferase activity was inhibited immediately by chloramphenicol and rifamycin, added at the beginning of growth or during mid-logarithmic growth. Low concentrations of chloramphenicol inhibited cellular protein synthesis and the accumulation of extracellular glucosyltransferase activity to the same extent, indicating a close coupling between glucosyltransferase synthesis and secretion. Experiments using cell lysates showed that no intracellular accumulation of glucosyltransferase activity occurred in the presence of the inhibitors and that the intracellular activity is very low relative to the cell-surface activity. The utilization of cells depleted of cell-associated glucosyltransferase activity indicated that most of the cell-associated glucosyltransferase activity does not act as a precursor for the extracellular enzyme. Sugar analogue inhibitors of glycoprotein synthesis did not have any specific effects on the synthesis or secretion of extracellular glucosyltransferase activity [responsible for glucan synthesis which is important in development of dental caries].