Co-induction of beta-galactosidase and the lactose-P-enolpyruvate phosphotransferase system in Streptococcus salivarius and Streptococcus mutans.

The addition of lactose, galactose, or isopropyl-beta-D-thiogalactoside (IPTG) to glucose-grown cells of Streptococcus salivarius 25975 resulted in the co-induction of both the lactose-P-enolpyruvate phosphotransferase system (lactose-PTS) and beta-galactosidase, with the latter the predominant metabolic system. With various strains of Streptococcus mutans and Streptococcus sanguis 10556, on the other hand, the lactose-PTS was the major metabolic pathway with beta-galactosidase induced either to low or negligible levels. In all cases, induction of the lactose-PTS resulted in the concomitant induction of 6-P-beta-galactosidase. The induction by lactose of both the lactose-PTS and beta-galactosidase in all strains was repressed by glucose and other catabolites, notably, fructose. Induction of beta-galactosidase in S. salivarius 25975 by IPTG was, however, relatively resistant to glucose repression. Induction experiments with IPTG and lactose suggested that a cellular metabolite of lactose metabolism was a repressor of enzyme activity. Exogenous cAMP was shown to reverse the transient repression by glucose of beta-galactosidase induction in cells of S. salivarius 25975 receiving lactose, provided the cells were grown with small amounts of toluene to overcome the permeability barrier to this nucleotide, cAMP, was however, unable to overcome the permanent repression of beta-galactosidase activity to a significant extent under these conditions.     

Environmental pH as a factor in the competition between strains of the oral streptococci Streptococcus mutans, S. sanguis, and "S. mitior" growing in continuous culture

Strains of Streptococcus mutans (biotype 1), Streptococcus sanguis, and Streptococcus mitior have been grown in mixed continuous culture in a semidefined medium under glucose limitation at a growth rate of D = 0.1 h-1. The effect of varying the environmental pH on the proportions of the different populations within the community has been determined. Initially the populations were allowed to reach steady state at pH 7.0 when S. sanguis was dominant with S. mutans and "S. mitior" maintaining similar populations. The medium pH was then lowered in steps of 0.5 pH units from pH 7.0 to 4.5, and the community was grown at each step for at least 15 generations. Viable counts of each species were made at 24-h intervals. The population ratios established at pH 7.0 remained relatively stable when the environmental pH was set at pH 6.5. However, after the medium pH was lowered to 6.0 (days 18-27), the population of S. mutans began to increase and the S. mitior population began to decline. A further change was seen at pH 5.5 (days 27-34) when S. mutans became dominant, S. sanguis declined, and S. mitior was not detectable. At pH 4.5, both S. mutans and S. sanguis were reduced in numbers, but survived until the experimental run was terminated (44 days). Samples of culture fluid were taken throughout the experiment and analyzed for the presence of the acid products of glucose metabolism. The amounts of lactic acid produced by the community increased as the environmental pH was lowered.(ABSTRACT TRUNCATED AT 250 WORDS)     

Application of a competition model to the growth of Streptococcus mutans and Streptococcus sanguis in binary continuous culture.

Streptococcus mutans 6715-15 and Streptococcus sanguis 10558 were grown together in continuous culture with glucose as the limiting carbon source. The relationship of growth rate to substrate concentration was determined for pure cultures of each organism in continuous and batch cultures. A model based on competition for a growth-limiting substrate (glucose) was used to predict the proportions of each organism when grown in binary cultures. The results indicate that interactions other than competition for glucose carbon exist between S. mutans and S. sanguis grown under these conditions.     

Physico-chemical surface characteristics and adhesive properties of Streptococcus salivarius strains with defined cell surface structures

Physico-chemical surface characteristics and adhesive properties of a series of mutants of Streptococcus salivarius HB with defined cell surface structures were determined. Zeta potentials showed no relation either with the presence or absence of specific antigens on the bacterial cell surface, or with the adhesive properties of the cells. Hydrophobicity was assessed by surface free energy determination from measured contact angles, by adsorption to hexadecane and by hydrophobic interaction chromatography. Generally, the progressive removal of fibril subclasses from the cell surface resulted in a reduced hydrophobicity. However, specific fibrillar subclasses appeared to contribute to surface hydrophobicity to widely different extents. Bacterial adhesion to polymethylmethacrylate increased with increasing hydrophobicity of the mutants. However, adhesion to a more complex biological substratum, such as saliva-coated hydroxyapatite, correlated only partly with hydrophobicity. The organism, deprived of most of its fibrillar surface structures, clearly showed the least adhesion to hydrophobic ligands, to both polymethylmethacrylate and saliva-coated hydroxyapatite, and had a significantly higher surface free energy than the other mutants and the parent strain.     

Regulation of ATP-dependent P-(Ser)-HPr formation in Streptococcus mutans and Streptococcus salivarius.

Sugar transport via the phosphoenolpyruvate (PEP) phosphotransferase system involves PEP-dependent phosphorylation of the general phosphotransferase system protein, HPr, at histidine 15. However, gram-positive bacteria can also carry out ATP-dependent phosphorylation of HPr at serine 46 by means of (Ser)HPr kinase. In this study, we demonstrate that (Ser)HPr kinase in crude preparations of Streptococcus mutans Ingbritt and Streptococcus salivarius ATCC 25975 is membrane associated, with pH optima of 7.0 and 7.5, respectively. The latter organism possessed 7- to 27-fold-higher activity than S. mutans NCTC 10449, GS-5, and Ingbritt strains. The enzyme in S. salivarius was activated by fructose-1,6-bisphosphate (FBP) twofold with 0.05 mM ATP, but this intermediate was slightly inhibitory with 1.0 mM ATP at FBP concentrations up to 10 mM. Similar inhibition was observed with the enzyme from S. mutans Ingbritt. A variety of other glycolytic intermediates had no effect on kinase activity under these conditions. The activity and regulation of (Ser)HPr kinase were assessed in vivo by monitoring P-(Ser)-HPr formation in steady-state cells of S. mutans Ingbritt grown in continuous culture with limiting glucose (10 and 50 mM) and with excess glucose (100 and 200 mM). All four forms of HPr [free HPr, P approximately (His)-HPr, P-(Ser)-HPr, and P approximately (His)-P-(Ser)-HPr] could be detected in the cells; however, significant differences in the intracellular levels of the forms were apparent during growth at different glucose concentrations. The total HPr pool increased with increasing concentrations of glucose in the medium, with significant increases in the P-(Ser)-HPr and P approximately HHis)-P-(Ser)-HPr concentrations. For example, while total PEP-dependent phosphorylation [P approximately(His)-HPr plus P approximately (His)-P-(Ser)-HPr] varied only from 21.5 to 52.5 microgram mg of cell protein (-1) in cells grown at the four glucose concentrations, the total ATP-dependent phosphorylation [P-(Ser)-HPr plus P approximately (His)-P-(Ser)-HPr] increased 12-fold from the 10 mM glucose-grown cells (9.1 microgram mg of cell protein (-1) to 106 and 105 microgram mg(-1) in the 100 and 200 mM glucose-grown cultures, respectively. (Ser)HPr kinase activity in membrane preparations of the cells varied little between the 10, 50, and 100 mM glucose-grown cells but increased threefold in the 200 mM glucose-grown cells. The intracellular levels of ATP, glucose-6-phosphate, and FBP increased with external glucose concentration, with the level of FBP being 3.8-fold higher for cells grown with 200 mM glucose than for those grown with 10 mM glucose. However, the variation in the intracellular levels of FBP, particularly between cells grown with 100 and 200 mM glucose, did not correlate with the extent of P-(Ser)-HPr formation, suggesting that the activity of (Ser)HPr kinase is not critically dependent on the availability of intracellular FBP.     

Reclassification of Peptostreptococcus magnus (Prevot 1933) Holdeman and Moore 1972 as Finegoldia magna comb. nov. and Peptostreptococcus micros (Prevot 1933) Smith 1957 as Micromonas micros comb. nov.

Several lines of evidence, notably 16S rRNA sequence analysis, indicate that the genusPeptostreptococcus is phylogenetically incoherent. Two of the most well studied species, Peptostreptococcus magnus and Peptostreptococcus micros, differ significantly in both genetic and phenotypic characteristics from each other and from the type species of the genus, Peptostreptococcus anaerobius. Therefore, we propose thatPeptostreptococcus magnus be reclassified in a new genus, Finegoldia, as Finegoldia magna; we propose that Peptostreptococcus micros be reclassified in new genus, Micromonas, as Micromonas micros.     

Application of a competition model to the growth of Streptococcus mutans and Streptococcus sanguis in binary continuous culture

Streptococcus mutans 6715-15 and Streptococcus sanguis 10558 were grown together in continuous culture with glucose as the limiting carbon source. The relationship of growth rate to substrate concentration was determined for pure cultures of each organism in continuous and batch cultures. A model based on competition for a growth-limiting substrate (glucose) was used to predict the proportions of each organism when grown in binary cultures. The results indicate that interactions other than competition for glucose carbon exist between S. mutans and S. sanguis grown under these conditions.     

Plaque formation in vitro by Actinomyces viscosus in the presence of Streptococcus sanguis or Streptococcus mutans.

Actinomyces viscosus, growing on a tooth in the presence of sucrose, slowly produced a loosely-attached plaque, the pH being 6.1 after 120 h. When the tooth was inoculated simultaneously with A. viscosus and either Streptococcus sanguis or Streptococcus mutans, firmly-adherent plaque was quickly formed and the pH fell below 5 after 33 h with the former Streptococcus and 24 h with the latter. A. viscosus disappeared from each mixed plaque by 120 h.     

The effect of oxygen on the growth and acid production of Streptococcus mutans and Streptococcus sanguis

Abstract Pure cultures of Streptococcus mutans NCTC 10499 and Streptococcus sanguis ATCC10556 were grown in a glucose-limited chemostat under varying concentrations of oxygen in the gas phase. Both streptococci consumed large amounts of oxygen by the partial oxidation of sugars, thus maintaining an anaerobic environment. With increasing oxygen concentrations the degradation products from glucose become more oxidized. Ethanol gradually disappeared from the culture fluid while the acetate concentration increased. In the case of S. sanguis , the products became even more oxidized at higher oxygen concentrations, and carbon dioxide was formed instead of formate. Sudden increase in the oxygen concentration in the gas phase caused elevated oxygen tensions in the cultures, which led to a decrease in the growth rate of the streptococci.     

载银纳米二氧化钛树脂基托对口腔变形链球菌、白色念珠菌和血链球菌的影响

目的研究载银纳米二氧化钛(Ag-TiO2)树脂基托对变形链球菌和白色念珠菌的体外抗菌效果,同时研究其对口腔有益菌血链球菌的影响。方法将不同质量分数的载银纳米二氧化钛抗菌粉剂添加到树脂基托材料中,制成抗菌树脂基托。采用薄膜密贴法分别检测该抗菌树脂基托对变形链球菌、白色念珠菌和血链球菌的抗菌率。结果与空白对照相比,Ag-TiO2质量分数为2.0%时,抗菌树脂基托对变形链球菌的抗菌率达95.0%,当质量分数达到3.0%时,抗菌率达到99.0%;Ag-TiO2质量分数为3.0%时,抗菌树脂基对白色念珠菌抗菌率达90.0%以上,但当Ag-TiO2质量分数达到5.0%时,仍未达到强抗菌作用;含Ag-TiO2的抗菌树脂基托对口腔有益菌血链球菌也存在一定的抑制作用,当Ag-TiO2质量分数达到5.0%,时抗菌树脂基托对变形链球菌的抗菌率达到51.6%。结论质量分数为3.0%的载银纳米二氧化钛树脂基托对变形链球菌、白色念珠菌均有抑制作用,对口腔血链球菌的杀灭作用不强,3.0%的浓度在既能杀死致病菌的同时又能最大程度保护口腔有益菌,可以很大程度上保证口腔微生态的平衡。     

Aspartokinase of Streptococcus mutans: purification, properties, and regulation.

Aspartokinase from Streptococcus mutans BHT was purified to homogeneity and characterized. The molecular weight of the native enzyme was estimated to be 242,000 by gel filtration. Cross-linking of aspartokinase with dimethyl suberimidate and polyacrylamide gel electrophoresis of the amidinated enzyme in the presence of sodium dodecyl sulfate showed the enzyme to be composed of six identical subunits with a molecular wieght of 40,000. The optimal pH range for enzyme activity was 6.5 to 8.5. The apparent Michaelis-Menten constants for aspartate and ATP were 5.5 and 2.2 mM, respectively. The enzyme was stable within the temperature range of 10 to 35 degrees C. Aspartokinase was not feedback inhibited by individual amino acids, but was concertedly inhibited by L-lysine and L-threonine (93.5% inhibition at 10 mM each). The inhibition was noncompetitive with respect to aspartate (Ki = 10 mM) and mixed with respect to ATP. L-Threonine methyl ester and L-threonine amide were able to substitute for L-threonine in feedback inhibition, but the requirement for L-lysine uas strict. The feedback inhibitor pair protected the enzyme against heat denaturation. Aspartokinase synthesis was repressed by L-threonine; this repression was enhanced by L-lysine, but was slightly attenuated by L-methionine.     

Fermentation of milk by Streptococcus salivarius subspecies salivarius and Streptococcus salivarius subspecies thermophilus and their use to the yoghurt manufacturer

Unlike Streptococcus salivarius subspecies thermophilus, Streptococcus salivarius subspecies salivarius fails to grow symbiotically in milk in the presence of Lacto-bacillus bulgaricus , does not produce large quantities of the flavour volatiles, acetal-dehyde or diacetyl and is unable to stimulate growth of Lact. bulgaricus by producing formate. Although Strep, salivarius subspecies salivarius and thermophilus have similar DNA base composition and belong in the same DNA homology group, the former is unsuitable for milk fermentations such as yoghurt because fermentation of milk using this organism results in products with poor flavour, aroma and texture.     

Inhibition of Streptococcus mutans NS adhesion to glass with and without a salivary conditioning film by biosurfactant- releasing Streptococcus mitis strains

The release of biosurfactants by adhering microorganisms as a defense mechanism against other colonizing strains on the same substratum surface has been described previously for probiotic bacteria in the urogenital tract, the intestines, and the oropharynx but not for microorganisms in the oral cavity. Two Streptococcus mitis strains (BA and BMS) released maximal amounts of biosurfactants when they were grown in the presence of sucrose and were harvested in the early stationary phase. The S. mitis biosurfactants reduced the surface tensions of aqueous solutions to about 30 to 40 mJ m(-2). Biochemical and physicochemical analyses revealed that the biosurfactants released were glycolipids. An acid-precipitated fraction was extremely surfactive and was identified as a rhamnolipidlike compound. In a parallel-plate flow chamber, the number of Streptococcus mutans NS cells adhering to glass with and without a salivary conditioning film in the presence of biosurfactant-releasing S. mitis BA and BMS (surface coverage, 1 to 4%) was significantly reduced compared with the number of S. mutans NS cells adhering to glass in the absence of S. mitis. S. mutans NS adhesion in the presence of non-biosurfactant-releasing S. mitis BA and BMS was not reduced at all. In addition, preadsorption of isolated S. mitis biosurfactants to glass drastically reduced the adhesion of S. mutans NS cells and the strength of their bonds to glass, as shown by the increased percentage of S. mutans NS cells detached by the passage of air bubbles through the flow chamber. Preadsorption of the acid-precipitated fraction inhibited S. mutans adhesion up to 80% in a dose-responsive manner. These observations indicate that S. mitis plays a protective role in the oral cavity and protects against colonization of saliva-coated surfaces by cariogenic S. mutans.     

Peptidoglycan composition and taxonomy of group D, E, and H streptococci, and Streptococcus mutans

The qualitative and quantitative composition of the peptidoglycan from the cell wall of groups D, E, and H streptococci, and Streptococcus mutans, was determined. In group D, S. faecalis and the closely related species S. liquefaciens and S. zymogenes were separated from S. faecium and the closely related species S. durans on the basis of their peptidoglycan composition. A relationship among S. bovis, S. equinus, and some strains of S. mutans was indicated by the presence in each of a similar peptidoglycan containing threonine. Threonine was released from the S. mutans polymer as a threonine-lysine dipeptide. Hydrolysis of the dipeptide at 100 C for 24 hr in 6 n HC1 was required to break the peptide bond. Motile group D streptococci possessed a peptidoglycan of the same composition as S. faecium. Group E and H strains were also similar in the composition of their peptidoglycan. The results demonstrate that peptidoglycan composition can be used to (i) aid in the division of members of an immunological group into subgroups, and (ii) indicate a relationship between members of the same genus which are not related on an immunological basis.     

Inhibition of Streptococcus mutans NS Adhesion to Glass with and without a Salivary Conditioning Film by Biosurfactant- Releasing Streptococcus mitis Strains

The release of biosurfactants by adhering microorganisms as a defense mechanism against other colonizing strains on the same substratum surface has been described previously for probiotic bacteria in the urogenital tract, the intestines, and the oropharynx but not for microorganisms in the oral cavity. Two Streptococcus mitis strains (BA and BMS) released maximal amounts of biosurfactants when they were grown in the presence of sucrose and were harvested in the early stationary phase. The S. mitis biosurfactants reduced the surface tensions of aqueous solutions to about 30 to 40 mJ m⁻². Biochemical and physicochemical analyses revealed that the biosurfactants released were glycolipids. An acid-precipitated fraction was extremely surfactive and was identified as a rhamnolipidlike compound. In a parallel-plate flow chamber, the number of Streptococcus mutans NS cells adhering to glass with and without a salivary conditioning film in the presence of biosurfactant-releasing S. mitis BA and BMS (surface coverage, 1 to 4%) was significantly reduced compared with the number of S. mutans NS cells adhering to glass in the absence of S. mitis. S. mutans NS adhesion in the presence of non-biosurfactant-releasing S. mitis BA and BMS was not reduced at all. In addition, preadsorption of isolated S. mitis biosurfactants to glass drastically reduced the adhesion of S. mutans NS cells and the strength of their bonds to glass, as shown by the increased percentage of S. mutans NS cells detached by the passage of air bubbles through the flow chamber. Preadsorption of the acid-precipitated fraction inhibited S. mutans adhesion up to 80% in a dose-responsive manner. These observations indicate that S. mitis plays a protective role in the oral cavity and protects against colonization of saliva-coated surfaces by cariogenic S. mutans.     

Purification and properties of pyruvate kinase from Streptococcus mutans.

Pyruvate kinase (EC 2.7.1.40) from Streptococcus mutans strain JC2 was purified, giving a single band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The molecular weight of the native enzyme was 180,000 to 190,000, and the enzyme was considered to consist of four identical subunits. This enzyme was completely dependent on glucose 6-phosphate for activity, and the saturation curve for activation by glucose 6-phosphate was sigmoidal. In the presence of 0.5 mM glucose 6-phosphate, the saturation curves for the substrates phosphoenolpyruvate and ADP were hyperbolic, and the Km values were 0.22 and 0.39 mM, respectively. GDP, IDP, and UDP could replace ADP, and the Km for GDP (0.026 mM) was 0.067 of that for ADP. The enzyme required not only divalent cations, Mg2+ or Mn2+, but also monovalent cations, K+ or NH4+, for activity, and it was strongly inhibited by Pi. When the concentration of Pi was increased, the half-saturating concentration and Hill coefficient for glucose 6-phosphate increased. However, the enzyme was immediately inactivated in a solution without Pi. The intracellular concentration of glucose 6-phosphate, in cooperation with that of Pi, may regulate pyruvate kinase activity in S. mutans.