Phenotypic stability of the cell wall of Streptococcus mutans Ingbritt grown under various conditions

Fueling the caries process: carbohydrate metabolism and gene regulation by Streptococcus mutans

The nature of the oral cavity and host behaviors has mandated that the oral microbiota evolve mechanisms for coping with environmental fluctuations, especially changes in the type and availability of carbohydrates. In the case of human dental caries, the presence of excess carbohydrates is often responsible for altering the local environment to be more favorable for species associated with the initiation and progression of disease, including Streptococcus mutans. Some of the earliest endeavors to understand how cariogenic species respond to environmental perturbations were carried out using chemostat cultivation, which provides fine control over culture conditions and bacterial behaviors. The development of genome-scale methodologies has allowed for the combination of sophisticated cultivation technologies with genome-level analysis to more thoroughly probe how bacterial pathogens respond to environmental stimuli. Recent investigations in S. mutans and other closely related streptococci have begun to reveal that carbohydrate metabolism can drastically impact pathogenic potential and highlight the important influence that nutrient acquisition has on the success of pathogens; inside and outside of the oral cavity. Collectively, research into pathogenic streptococci, which have evolved in close association with the human host, has begun to unveil the essential nature of careful orchestration of carbohydrate acquisition and catabolism to allow the organisms to persist and, when conditions allow, initiate or worsen disease.

Fermentation products, amino acid utilization, maintenance energies and growth yields for the fibrillar Streptococcus salivarius HB and a non-fibrillar mutant HB-B grown in continuous culture under glucose limitation

The fibrillar strain Streptococcus salivarius HB and a non-fibrillar mutant, strain HB-B, were grown in a defined medium under glucose limitation in a chemostat. Fermentation balances were produced for both strains in batch culture and at growth rates between 0.1/h and 1.1/h. In batch culture both strains fermented glucose to lactate, but in continuous culture glucose was fermented to formate, acetate and ethanol with increasing amounts of lactate as the growth rate was increased. Lactate never became the major fermentation product even at the highest growth rate. Amino acid analysis showed that only lysine was more than 50% utilized, while proline and tyrosine showed net production. The non-fibrillar strain HB-B showed, in general, a reduced utilization of amino acids compared with the fibrillar strain HB. Calculated growth yields and maintenance energies for the two strains showed that there was a reduction in the true growth yield and the maintenance energy coefficient of the non-fibrillar strain HB-B when compared with the fibrillar strain HB. The increase in the maintenance energy of the fibrillar strain HB (1.382 mmol/g/h) when compared with the non-fibrillar strain HB-B (0.546 mmol/g/h) of 153% is proposed to be the energy required for the maintenance of the fibrillar surface of the cell.

Quantitative analysis of cell walls of nutritionally variant streptococci grown under various growth conditions

Strains of nutritionally variant streptococci are usually isolated from patients with subacute bacterial endocarditis. Only recently have these strains been subdivided into three serotypes; however, no group-specific antigen has been described. To understand the immunochemical basis for the serology of these microorganisms as well as set the groundwork for adherence studies, quantitative analysis of the cell walls of nutritionally variant streptococci was undertaken. The bacteria were grown in semisynthetic medium or pyridoxal-supplemented Todd-Hewitt broth and harvested during the exponential or stationary phase. Cell walls were isolated and analyzed for amino sugars, sugars, polyalcohols, amino acids, and phosphorus by gas chromatography, high-pressure liquid chromatography, or colorimetric assays. The peptidoglycans of the cell walls of the prototype strains from the three serotypes were representative of other streptococcal cell walls, including the presence of alanine as the possible cross-bridge. The composition of the peptidoglycan was similar for all three strains and included a decreased concentration of peptidoglycan in their cell walls during the stationary phase. Glucosamine, glucose, galactose, ribitol, and a small amount of rhamnose were found in each of the cell wall polysaccharides. Galactosamine was only found in serotype II and III cell walls and might be responsible for the previously described cross-reaction between these strains. The concentration of the other sugars and amino sugars varied in each of the cell wall preparations, depending on the growth conditions. Finally, all three strains expressed both ribitol and phosphorus in their cell walls, characteristic of the presence of a ribitol teichoic acid. Therefore the cell wall composition of the nutritionally variant streptococci varies depending on the growth conditions, and their composition appears similar to that of strains of Streptococcus mitis.

31P-NMR studies of the oral pathogen Streptococcus mutans: observation of lipoteichoic acid

We have used 31P-nuclear magnetic resonance spectroscopy to identify phosphorus-containing compounds in whole cells of two serotype c strains of the oral pathogen Streptococcus mutans. The major resonance, centered at 0 ppm in whole cells, was attributed to lipoteichoic acid on the basis of its chemical shift, insensitivity to pH changes, cellular localization and a comparison with spectra obtained with purified lipoteichoic acid from S. mutans. The linewidths of resonances observed for intact cells and purified lipoteichoic acid were moderately narrowed by increasing the ionic strength, and substantially broadened in the presence of the lectin concanavalin A. Experiments with purified lipoteichoic acid suggest that this compound in whole cells is complexed with divalent cations such as Mg2+. Intracellular pools of other phosphorus-containing metabolites were found to be low when compared to the lipoteichoic acid concentration in both starved and glycolyzing cells.

Characterization of polysaccharide antigens of Streptococcus mutans B13 grown under various conditions

Bacteria may respond to changes in their environment by varying the synthesis of surface components. This study examined the effects of various culture conditions on two wall polysaccharides of Streptococcus mutans B13 (serotype d): serotype d antigen, a galactose-glucose polymer, and RGP antigen, a rhamnose-glucose polymer. Cells were grown in a chemostat at various dilution rates (D) and pH values, including D = 0.05, 0.1, and 0.5 h-1 at pH 6.0 and D = 0.1 h-1 at pH 5.5, 6.0, 6.5, and 7.5. The cells were examined for protein and carbohydrate content by colorimetric assays and gas-liquid chromatography. Rantz-Randall extracts (120 degrees C, 30 min) and M-1 N-acetylmuramidase digests were prepared and examined for the presence of specific antigens by agar gel diffusion and quantitative precipitation assays. Cell preparations did not vary significantly with respect to total protein or carbohydrate content; however, cells grown at D = 0.1 h-1 and pH 7.5 had a significantly higher rhamnose content than did the other preparations. Rapidly growing cultures appeared to be more resistant to M-1 N-acetylmuramidase digestion than did slower-growing cultures. Agar gel diffusion studies demonstrated that both serotype d and RGP antigens were present in all samples, although significantly less RGP antigen was noted in the pH 7.5 culture. These observations were confirmed by quantitative precipitation assays. M-1 N-acetylmuramidase digests of the pH 7.5 culture were lacking in RGP precipitation activity although RGP inhibition activity was demonstrated. The data suggest that the cell content of serotype d antigen was relatively constant under the growth conditions tested, whereas the synthesis of RGP antigen was modified under conditions of high pH.

Biochemical and immunological differences between hydrophobic and hydrophilic strains of Streptococcus mutans

Hydrophobic strains of Streptococcus mutans were compared with paired variants showing reduced hydrophobicity. Extracts of hydrophobic cells contained a number of high-molecular-weight proteins which were not present on cells with decreased hydrophobicity. The proteins were found in purified cell walls, suggesting that they are located on the bacterial surface. Trypsin treatment of whole cells destroyed the proteins and reduced the hydrophobicity. Chemical analysis did not reveal any marked differences in the proportion of cell wall constituents. The amino acid compositions and lipoteichoic acid contents of hydrophobic and hydrophilic cell walls were similar. Culture supernatants from the hydrophilic variants contained high-molecular-weight proteins similar to those extracted from the cell walls of the hydrophobic parent strains, indicating that the variants were impaired in their ability to incorporate the hydrophobicity-associated proteins into the cell wall. The dominant protein had a molecular weight of 190,000, similar to that of antigen I/II (B) of S. mutans.

Streptococcal hyaluronic acid: proposed mechanisms of degradation and loss of synthesis during stationary phase

Streptococcal hyaluronic acid was found to distribute into two discrete sizes. Cellular hyaluronic acid from strain D181 had an average molecular weight of 10 X 10(6), whereas the average molecular weight of extracellular hyaluronic acid from the same strain was 2 X 10(6). Cellular streptococcal hyaluronic acid was purified to homogeneity. Proteases were unable to cleave the purified cellular polymer, indicating that a peptide was not involved in cross-linking five extracellular hyaluronate polymers to form a cell-bound complex. Lipids apparently are not part of the cellular hyaluronic acid because phosphorus and glycerol were not detected by radioisotopic techniques, and denaturing conditions did not change the size of the polymer. Membranes obtained from various strains of group A and C streptococci cleaved the cellular form of the hyaluronate polymer demonstrating the presence of a membrane-bound hyaluronidase-like activity. By contrast, this activity was not found in the extracellular products of the strains studied. Furthermore, membranes derived from streptococci at the stationary phase of growth no longer had the capacity to synthesize hyaluronic acid. The loss of this property appeared to be due to changes in the structure of the membrane.

Detection of antigens in enzymic lysates of cell wall from Streptococcus mutans strains

Lysis of cell wall preparations from strains representing serotypes a - g of Streptococcus mutans has provided a convenient and efficient means of obtaining the typing antigens in a soluble undegraded form, and has demonstrated that, in each case, the antigen is a cell wall component in the strict sense of a component joined covalently to peptidoglycan. This influences the choice of extraction procedures.

Characterization of serological cross-reactivity between polysaccharide antigens of Streptococcus mutans serotypes c and d

Immunological assays with antisera prepared against purified Streptococcus mutans serotype c polysaccharide demonstrated that a cross-reacting determinant on c polysaccharide reacted with the wall-associated rhamnose-glucose polysaccharide from S. mutans serotype d. Studies with 60 antisera prepared against chemostat cultures of S. mutans Ingbritt (c) demonstrated that the rhamnose-glucose polysaccharide cross-reactive determinant was consistently expressed on c antigen under a variety of growth conditions.

Effect of growth conditions on production of rhamnose-containing cell wall and capsular polysaccharides by strains of Lactobacillus casei subsp. rhamnosus

Strains of Lactobacillus casei subsp. rhamnosus possessing two cell wall polysaccharides, a hexosamine-containing H-polysaccharide and a rhamnose-containing R-polysaccharide, were examined for the effect of growth conditions on the production of these two components. In strain NCTC 6375, R- and H-polysaccharides accounted for an estimated 44 and 20%, respectively, of the cell wall for organisms grown in batch culture with glucose as the carbohydrate source. Growth on fructose-containing media reduced the amount of R-polysaccharide by approximately 50% without affecting the amount of H-polysaccharide. Subculture of fructose-grown organisms in glucose restored the original proportions of the two polysaccharides. Galactose- and sucrose-grown cells behaved similarly to glucose-grown cells with respect to polysaccharide production, whereas growth in rhamnose or ribose showed values close to those for fructose-grown cells. Continuous culture of strain NCTC 6375 for more than 100 generations showed a gradual and irreversible reduction of the R-polysaccharide to less than 5% of the cell wall and an increase of the H-polysaccharide to 40% of the cell wall. Other type culture strains of L. casei subsp. rhamnosus, NCIB 7473 and ATCC 7469, behaved similarly in batch and continuous culture. In contrast, strains of L. casei subsp. rhamnosus isolated at the Institute of Dental Research showed phenotypic stability with respect to the relative proportions of R- and H-polysaccharides in both batch and continuous culture. Changes in polysaccharide composition of type culture strains were also mirrored in changes in the immunogenicity of the two components and resistance to the rate of enzymic lysis of whole organisms. For L. casei subsp. rhamnosus strain NCTC 10302 the R-polysaccharide is present entirely as capsular material. The amount of R-polysaccharide produced was also markedly dependent on the carbohydrate component of the medium in batch culture and both dilution rate and nature of the limiting carbohydrate in continuous culture, varying over a 10-fold range, whereas the cell wall H-polysaccharide remained constant.

Isolation and characterization of Streptococcus mutans mutants with altered cellular morphology or chain length

A nitrosoguanidine-induced mutant, designated UAB90, of Streptococcus mutans PS14 (serotype c) strain UAB62, was identified on the basis of its unique colony morphology and isolated on brain heart infusion agar. Other mutants displaying similar colony morphologies on brain heart infusion agar were isolated after ethyl methane sulfonate mutagenesis of UAB62 and S. mutans 6715 (serotype g) strains UAB61 and UAB66, and these were found to exhibit abnormalities in cell morphology, chain length, or both. All mutants were examined further for (i) adherence and aggregation after overnight growth in medium containing sucrose, (ii) growth and aggregation in brain heart infusion broth and medium containing glucose, (iii) aggregation of nongrowing cells in the presence of 2 mg of sucrose per ml or 200 mug of dextran per ml, (iv) dextranase activity, and (v) ease of cell lysis. Mutants isolated included several with long chains of enlarged cocci, and two of these strains, UAB261 and UAB433, along with UAB90, were more susceptible to cell lysis than were their parents. UAB261, isolated from UAB62, maintained other parental characteristics, whereas UAB433, isolated from UAB66, lost its ability to aggregate in the presence of either sucrose or dextran. The "fragile" mutant UAB90 was particularly useful in the isolation of high-molecular-weight DNA for early gene cloning experiments by our laboratory. Two other cell morphology mutants, UAB272 from UAB66 and UAB289 from UAB61, did not lyse better than their parents, but both lacked measurable dextranase activity. A final mutant, UAB276 from UAB66, displayed only increased chain length without apparent cell morphology variations. Chains produced by this mutant were up to 10 times longer than those produced by UAB66. UAB276 lysed slightly less well than its parent but retained all other wild-type characteristics examined.

Teichoic acids from chemostat-grown cultures of Streptococcus mutans and Lactobacillus plantarum

We examined the effect of growth conditions in chemostat culture on the quantity and composition of the cell wall teichoic acids of Streptococcus mutans BHT and Lactobacillus plantarum NCIB 7220 and the membrane lipoteichoic acid from S. mutans Ingbritt. With the cell wall teichoic acids, which are covalently linked to peptidoglycan, the amount of teichoic acid is independent of the growth conditions employed. However, the extent of glucosyl substitution of the polymer from L. plantarum was dependent on growth conditions. S. mutans Ingbritt lipoteichoic acid, on the other hand, was little affected by growth conditions in terms of composition or serological activity, but the amount produced was markedly affected by changes in growth conditions.

Chemostat studies of the effect of environmental control on Streptococcus sanguis adherence to hydroxyapatite

Streptococcus sanguis is a major component of early dental plaque. The ability of S. sanguis to adhere to salivary pellicle appears to involve specific bacterial surface receptors. The nature of these receptors is still not known; however, the component molecules may be subject to environmental control as has been shown for teichoic acids and certain proteins. To study these environmental effects, a chemostat was employed to vary the growth conditions of Streptococcus sanguis strain G9B. This strain has been used extensively to study the adhesion of [(3)H]thymidine-labeled batch-grown cells to saliva-coated hydroxyapatite beads. The effects of dilution rate, pH, and carbon source on adhesion were studied with a competition assay in which the labeled batch cells were used as a reference standard. In this assay, cells from the chemostat were harvested and compared for their ability to inhibit adhesion of labeled cells relative to unlabeled control batch-grown cells. Subsequent studies used chemostat grown cells labeled with [(3)H]thymidine as a reference standard so that results were internally controlled and reflected only the particular alteration in environment which was studied. These results indicated that when glucose was used as a growth-limiting substrate, cells grown at relatively high dilution rates (D = 0.5 h(-1); mean generation time = 1.4 h) behaved similarly to batch-grown cells and appeared to compete for the same binding sites. Cells grown at D = 0.1 h(-1) (mean generation time = 7 h) no longer competed with either batch-grown cells or chemostat cells grown at D = 0.5 h(-1). Moreover, adsorption isotherms of such slow-growing cells (D = 0.1 h(-1)) suggested that binding was no longer specific. When fructose was used as the growth-limiting carbohydrate, cells grown at D = 0.1 h(-1) did not show this loss of specificity and competed nearly as well as control batch-grown glucose cells. However, the effect of pH appeared to be independent of carbohydrate source, because cells grown in either glucose or fructose at pH 5.5 at D = 0.1 h(-1) lost the ability to compete with reference batch or chemostat cells grown at D = 0.5 h(-1). This effect was very sharp, since cells grown in the pH range from 6 to 7.5 at D = 0.5 h(-1) competed nearly as well as control cells. A similar effect of pH was found for batch cultures grown with excess glucose. These studies reinforce the idea that the environment can profoundly affect the bacterial surface and consequently the ability of the organism to adhere, a property which appears to be a primary event in some infectious diseases and in dental plaque formation.

Effect of fructose and other carbohydrates on the surface properties, lipoteichoic acid production, and extracellular proteins of Streptococcus mutans Ingbritt grown in continuous culture

Streptococcus mutans Ingbritt was grown in a chemostat at destined dilution rates in either 0.5% fructose or 0.5% sorbitol and at destined pH values in 0.5% fructose. The yield of cells was affected by the carbohydrate source, as well as by the pH, with the lowest yield being at pH 5.5 in 0.5% fructose. Fructose-grown cells showed greater susceptibility to lysis by a muramidase than the corresponding glucose-grown cells, but there were no marked differences in the lytic susceptibilities of the corresponding cell wall preparations or in the serological reactivities of wall lysates with antiserum to S. mutans Ingbritt. The greatest amounts of cellular lipoteichoic acid were obtained at high dilution rates in both fructose and sorbitol, as well as at high pH values in fructose. The greatest amounts of extracellular lipoteichoic acid were found at low dilution rates, as estimated by rocket immunoelectrophoresis and also by hemagglutination. Three major extracellular protein components were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and the effects of growth conditions on these components were determined. Results for batch-grown cultures showed that there was genotypic variation in the susceptibility of cells to lysis by a muramidase. The enhancement of lipoteichoic acid production by fructose and sorbitol in batch cultures was not identical in representative strains of S. mutans serotype c, nor was the effect of fructose found uniformly in representative strains of the different S. mutans serotypes.

Effect of carbohydrate source and growth conditions on the production of lipoteichoic acid by Streptococcus mutans Ingbritt

Streptococcus mutans Ingbritt was grown in a chemostat at defined dilution rates and pH values and under carbohydrate limitation. At a constant dilution rate of D = 0.1 h-1 and with either 0.5% glucose or 0.5% sucrose, the amounts of both cellular and extracellular lipoteichoic acid increased as the culture pH increased from 5.0 to 7.5. At a constant pH of 6.0, the amount of cellular lipoteichoic acid formed by cultures growing in 0.2% or 0.5% glucose was relatively constant over a range of dilution rates, although the amount of extracellular lipoteichoic acid formed in 0.2% glucose at intermediate dilution rates was less than that formed in 0.5% glucose. Organisms grown in 0.5% sucrose at pH 6.0 contained increasing amounts of cellular lipoteichoic acid as the dilution rate was increased. A comparison of the amounts of cellular lipoteichoic acid formed by organisms growing at D = 0.5 h-1 and pH 6.0 in glucose, sucrose, fructose, or mixtures of glucose and fructose in limiting amounts suggested that the enhanced production of lipoteichoic acic by sucrose-grown organisms was due to the fructose component. The culture fluids from both glucose- and sucrose-grown organisms contained detectable amounts of serotype c antigen, whereas glucose-grown cultures also contained significant amounts of an extracellular hexose-containing polymer.