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

Abstract

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.

Dissimilar Effects of Na+ and K+ on the Promotion of Glucosyltransferase Secretion in Streptococcus salivarius

“…For instance, the same level of GTF, expression occurred when S. sanguis was grown in a complex medium containing 100 mM-Na+ (undefined K+ concentration) as when it was grown in one containing 100 mM-K+ (undefined Na+ concentration) (West et al, 1987). This contrasts with previous reports that the secretion of GTF, in S. sanguis was inhibited by Na+ and that a high K+ concentration ( > 100 mM) as well as a high K+/Na+ ratio was necessary to ensure GTF, synthesis and secretion (Keevil et al, 1983(Keevil et al, ,1984. At face value these results with S. sanguis appear contrary to our own finding that a greater rate of GTF, expression occurred when S. salivarius was grown in Na+-rich medium (218 mM-Na+, 1-46 mM-K+) rather than semi-defined medium rich in K+ (31 mMNa+, 184 mM-K+) (Markevics & Jacques, 1985).…”

Rgg is a positive transcriptional regulator of the Streptococcus gordonii gtfG gene

“…The relevance of this work with respect to the previously reported Spp ϩ -Spp Ϫ phase variation phenomenon (22) is being investigated. It would be interesting to determine if there are specific physiological conditions similar to those described by other investigators for various streptococcal species (2,3,4,7,8,15,23,27) that affect expression of the S. gordonii Challis GTF enzyme and, if so, to determine the possible involvement of rgg.…”

Characterisation of and polysaccharide production by amoxycillin-resistant streptococci

“…However, using a specific assay, all strains were found to be capable of secreting glucosyltransferases that synthesise such extracellular glucans, although the activities of GTF-S, the enzyme responsible for dextran production, was lower in culture supernates of resistant strains than in that of an antibiotic-sensitive strain included as a control. This apparent paradox might be explained by the finding that, unlike S. mutans (Fukui et al, 1982), dextran synthesis by S. sanguis (Keevil et al, 1984), and particularly by our antibiotic-resistant strains, is markedly inhibited by low-molecularweight dextran primers. Sucrose can act as both substrate and inducer to some enzymes; therefore, the relatively high concentrations of this sugar in the TYC agar plates and in the broth cultures might have inhibited polysaccharide production.…”

“…l o ) activity Amoxycillin-resistant strains were grown in batch culture in a complex medium (LHP) containing potassium salts and supplemented with glucose 1 % w/v at a constant pH 7.0 by the automatic addition of 2M KOH (Keevil et al, 1984). The bacteria were grown until late log phase and the enzymes that synthesise glucans and fructans from sucrose were assayed in culture supernates in the presence and absence of dextran primers (60 pg/ml, final concentration) by the method of Keevil et al (1984). The enzymes that produce insoluble glucan (mutan) and insoluble fructan are GTF-I and FTF-I, respectively; activities were expressed as the amounts (pg) of insoluble glucan or fructan that were polymerised from sucrose (/ml of culture supernate)/h.…”