Inhibition of the Synthesis and Secretion of Extracellular Glucosyl- and Fructosyltransferase in Streptococcus sanguis by Sodium Ions

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Abstract
SUMMARY: The influence of Na+ and K+ on the synthesis and secretion of extracellular glucosyltransferase (GTF; EC 2.4.1.5) and fructosyltransferase (FTF; EC 2.4.1.10) by Streptococcus sanguis NCTC 7865 and Streptococcus sanguis 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.