SUMMARY: The influence of Na and K on the synthesis and secretion of extracellular glucosyltransferase (GTF; EC and fructosyltransferase (FTF; EC by NCTC 7865 and Challis NCTC 7868 has been determined. No FTF and little or no mutansucrase (GTF-I) activities were detectable during growth on glucose or sucrose unless the Na/K ratio of the cultures was kept low. Increasing K concentrations stimulated the production of FTF and dextransucrase (GTF-S), but all glycosyltransferase activities decreased in high K media when the growth pH was maintained with NaOH instead of KOH, indicating that the Na/K ratio effect was due principally to Na inhibition. Significant GTF and FTF activities were detected in a putative GTF mutant of strain Challis grown in high K medium but not in high Na medium, suggesting that the mutant might be defective in a regulatory gene.


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