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PubMed2005

Up-regulation of competence- but not stress-responsive proteins accompanies an altered metabolic phenotype in Streptococcus mutans biofilms.

Mature biofilm and planktonic cells of Streptococcus mutans cultured in a neutral pH environment were subjected to comparative proteome analysis. Of the 242 protein spots identified, 48 were significantly altered in their level of expression (P<0.050) or were unique to planktonic or biofilm-grown cells. Among these were four hypothetical proteins as well as proteins known to be associated with the maintenance of competence or found to possess a cin-box-like element upstream of their coding gene. Most notable among the non-responsive genes were those encoding the molecular chaperones DnaK, GroEL and GroES, which are considered to be up-regulated by sessile growth. Analysis of the rest of the proteome indicated that a number of cellular functions associated with carbon uptake and cell division were down-regulated. The data obtained were consistent with the hypothesis that a reduction in the general growth rate of mature biofilms of S. mutans in a neutral pH environment is associated with the maintenance of transformation without the concomitant stress response observed during the transient state of competence in bacterial batch cultures.

Adaptation, Physiological↗

PubMed1991

Acidogenesis in relation to fluoride resistance of Streptococcus mutans.

The velocity of acid production (Vap) of Streptococcus mutans C180-2 and of 2 fluoride-resistant mutant strains S. mutans C180-2FR and S. mutans C180-2MFR was examined in vitro at pH values between 7.0 and 4.5. The Vap of the fluoride-resistant mutants was lower than the Vap of the parent strain at pH greater than or equal to 6.0. At pH 5.5 and 5.0, the Vap of the mutant strains was higher than the Vap of the parent strain, whereas at pH 4.5 no significant differences were observed between the Vap of the 3 strains. The fluoride sensitivity of all 3 strains was amplified by a low pH environment. The fluoride concentration necessary to inhibit the acid production of the parent strain completely was 27 mM at pH 7 and 0.1 mM at pH 4.5. For the 2 mutants, the corresponding concentrations were 65 mM at pH 7 and 0.5-0.7 mM at pH 4.5. The results suggest that, if S. mutans acquires fluoride resistance in vivo, the rate of acid production in dental plaque may be decreased at pH greater than or equal to 6, but increased at lower pH levels. Low concentrations of fluoride inhibit acid production less effectively.

Dental Plaque↗

PubMed1985

The effect of penicillin on fatty acid synthesis and excretion in Streptococcus mutans BHT.

Treatment of exponentially growing cultures of Streptococcus mutans BHT with growth-inhibitory concentrations (0.2 microgram/ml) of benzylpenicillin stimulates the incorporation of [2-14C] acetate into lipids excreted by the cells by as much as 69-fold, but does not change the amount of 14C incorporated into intracellular lipids. At this concentration of penicillin cellular lysis does not occur. The radioactive label is incorporated exclusively into the fatty acid moieties of the glycerolipids. The increase in the radioactive content of the extracellular lipids reflects an actual net increase in the total fatty acid content as determined by a chemical assay. During a 4-hr incubation in the presence of penicillin, the extracellular fatty acid ester concentration (per mg cell dry weight) increases 1.5 fold, even though there is no growth or cellular lysis. No change is observed in the intracellular fatty acid ester content. An indication of the relative rate of fatty acid synthesis was most readily obtained by placing S. mutans BHT in a buffer containing 14C-acetate. Under these nongrowing conditions free fatty acids are the only lipids labeled, a factor which simplifies the assay. The addition of glycerol to the buffer causes all of the nonesterified fatty acids to be incorporated into glycerolipid. The cells excrete much of the lipid whether glycerol is present or not. Addition of penicillin to the nongrowth supporting buffer system does not stimulate the incorporation of [14C]-acetate into fatty acids.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetates↗

PubMed1979

Improved purification procedure for the extracellular D-glucosyltransferase from Streptococcus mutans 6715.

The exocellular D-glucosyltransferase from Streptococcus mutans 6715 has been highly purified with minimal loss of enzymic activity. The organisms were cultured in trypticase soy-broth that had been treated with invertase and filtered through an ultrafilter fitted with a membrane having a cut-off molecular weight at 10,000. To the growth medium was added Tween 80, which prevented the enzyme from aggregating. The final step in the purification employed insoluble, streptococcal dextran as an affinity support. Two D-glucosyltransferase activities were detected, viz., one that did not adsorb to the insoluble dextran and one that did. The enzymic fraction that had adsorbed to the insoluble dextran in the affinity column was strongly inhibited by added insoluble dextran.

Glucosyltransferases↗

PubMed1998

Diacylglycerol kinase is involved in regulation of expression of the lantibiotic mutacin II of Streptococcus mutans.

Genetic characterization of a Tn916 transposon mutant, Streptococcus mutans T8-1, defective in mutacin II production, revealed that the transposon was inserted into the 3' region of a diacylglycerol kinase (dgk) gene. The insertion occurred in the same region as described for another S. mutans mutant, GS5Tn1, which was altered in its ability to respond to environmental stress (Y. Yamashita, T. Takehara, and H. K. Kuramitsu, J. Bacteriol. 175:6220-6228, 1993). Quantitative primer extension from the mutacin structural gene mutA showed a decreased level (about eightfold) of mutA transcription for mutant T8-1. Mutacin production was restored by transforming mutant T8-1 with integration vector pVA891 containing an intact dgk gene. These data indicated that the full-length dgk gene product along with the mutacin biosynthetic operon are required for the production of the mutacin II lantibiotic.

Amino Acid Sequence↗

PubMed1980

Effect of sodium fluoride on the viability and growth of Streptococcus mutans.

A fluoride-sensitive (FS) strain of Streptococcus mutans and a laboratory-induced fluoride-resistant (FR) offspring were compared for the effects of sodium fluoride on viability and growth. There was a significant fluoride-related loss of viability in resting cell suspensions of the FS strain during a 47-hour exposure to fluoride levels above 75 ppm that was not encountered with the FR strain. The addition of 300 ppmF to actively growing six-hour broth cultures almost totally arrested the growth of the FS strain, while only slightly reducing that of the FR culture. The addition of 600 ppmF immediately terminated FS growth, and greatly reduced the rate and maximum growth of FR cultures.

Cell Division↗

PubMed2003

Cellular and extracellular proteome analysis of Streptococcus mutans grown in a chemostat.

The oral pathogen, Streptococcus mutans, was grown under glucose limitation in a chemostat at pH 7.0 and a dilution rate of 0.1 h(-1) to mimic the conditions prevailing in a healthy human oral cavity in between meal times. Solubilized cellular and extracellular proteins were separated by two-dimensional gel electrophoresis (2-DE) and, following tryptic digestion, 421 protein spots analyzed by matrix-assisted laser desorption/ionization-time of flight mass spectrometry or electrospray ionization-tandem mass spectrometry. Analyses of the mass spectral data showed that the proteins matched the translation products of 200 different open reading frames (ORFs) deduced from contigs of the S. mutans UA159 genome and thus represented proteins derived from approximately 11% of the total ORFs of the bacterium. Of the identified proteins, 172 (including one surface protein) were characterized in the cellular fraction, and the remaining 28 (including two surface proteins) were uniquely identified from the culture fluid. The expression and therefore the existence of 30 proteins previously designated as 'hypothetical' or with no known function was confirmed. 2-DE of whole cell lysates revealed only a single intrinsic membrane protein. This is consistent with proteomic analyses of other Gram-positive bacteria where hydrophilic proteins represent the vast majority of those characterized.

Amino Acid Sequence↗

PubMed2002

Analysis of Streptococcus mutans proteins modulated by culture under acidic conditions.

Streptococcus mutans, a major etiological agent of dental caries, causes demineralization of the tooth tissue due to the formation of acids from dietary carbohydrates. Dominant among the virulence determinants of this organism are aciduricity and acidogenicity, the abilities to grow at low pH and to produce acid, respectively. The mechanisms underlying the ability of S. mutans to survive and proliferate at low pH are currently under investigation. In this study we cultured S. mutans at pH 5.2 or 7.0 and extracted soluble cellular proteins. These were analyzed using high-resolution two-dimensional gel electrophoresis, and replicate maps of proteins expressed under each of the two conditions were generated. Proteins with modulated expression at low pH, as judged by a change in the relative integrated optical density, were excised and digested with trypsin by using an in-gel protocol. Tryptic digests were analyzed using matrix-assisted laser desorption ionization mass spectrometry to generate peptide mass fingerprints, and these were used to assign putative functions according to their homology with the translated sequences in the S. mutans genomic database. Thirty individual proteins exhibited altered expression as a result of culture of S. mutans at low pH. Up-regulated proteins (n = 18) included neutral endopeptidase, phosphoglucomutase, 60-kDa chaperonin, cell division proteins, enolase, lactate dehydrogenase, fructose bisphosphate aldolase, acetoin reductase, superoxide dismutase, and lactoylglutathione lyase. Proteins down-regulated at pH 5.2 (n = 12) included protein translation elongation factors G, Tu, and Ts, DnaK, small-subunit ribosomal protein S1P, large-subunit ribosomal protein L12P, and components of both phosphoenolpyruvate:protein phosphotransferase and multiple sugar binding transport systems. The identification of proteins differentially expressed following growth at low pH provides new information regarding the mechanisms of survival and has identified new target genes for mutagenesis studies to further assess their physiological significance.

Bacterial Proteins↗

PubMed1985

Inhibition of plaque and caries formation by a glucan produced by Streptococcus mutans mutant UAB108.

A mutant (UAB108) derived from Streptococcus mutans UAB66, a spectinomycin-resistant (Spcr) isolate of strain 6715, inhibited plaque formation when grown with strain 6715 in a sucrose medium and also inhibited caries formation in gnotobiotic rats infected with both strain UAB108 and 6715. A substance obtained from UAB108 culture supernatant fluid after ethanol precipitation and DEAE-cellulose treatment, designated glucan 108, inhibited S. mutans 6715 virulence and was shown to be a water-soluble glucan. In the presence of sucrose and increasing concentrations of glucan 108, the activity of a glucosyltransferase (GTase) preparation from S. mutans 6715 to synthesize adhesive water-insoluble glucan (ad-WIG) was inhibited, and the activity to synthesize non-ad-WIG was stimulated. Glucan 108 similarly inhibited sucrose-dependent adherence of heat-treated cells, was a poor inducer of cell aggregation, and inhibited S. mutans 6715-induced dental caries in gnotobiotic rats. In the presence of GTase, glucan 108, and sucrose, the glucose moiety of sucrose was found to be incorporated into glucan 108, and most of this glucose-incorporated glucan 108 was found in the non-ad-WIG fraction. The mode of inhibition of plaque formation by S. mutans 6715 appears to involve a shift from ad-WIG to non-ad-WIG formation. The water-soluble glucan 108 was found to have an approximate molecular weight of 2 X 10(6) and was hydrolyzed by fungal dextranase to yield glucans with an average molecular weight of about 1.2 X 10(4). This glucan (designated glucan 12k) was further hydrolyzed by bacterial dextranase to yield smaller glucans and oligosaccharides, but was refractile to alpha (1----3) glucanase. These results suggest that glucan 108 is a branched alpha (1----6) glucan, and it is proposed that UAB108 is defective in its ability to polymerize glucan 12k with alpha (1----3)-linked glucosyl residues.

Adhesiveness↗

PubMed2005

Genetic analysis of a unique bacteriocin, Smb, produced by Streptococcus mutans GS5.

A dipeptide lantibiotic, named Smb, in Streptococcus mutans GS5 was characterized by molecular genetic approaches. The Smb biosynthesis gene locus is encoded by a 9.5-kb region of chromosomal DNA and consists of seven genes in the order smbM1, -T, -F, -M2, -G, -A, -B. This operon is not present in some other strains of S. mutans, including strain UA159. The genes encoding Smb were identified as smbA and smbB. Inactivation of smbM1, smbA, or smbB attenuated the inhibition of the growth of the indicator strain RP66, confirming an essential role for these genes in Smb expression. Mature Smb likely consists of the 30-amino-acid SmbA together with the 32-amino-acid SmbB. SmbA exhibited similarity with the mature lantibiotic lacticinA2 from Lactococcus lactis, while SmbB was similar to the mersacidin-like peptides from Bacillus halodurans and L. lactis. We also demonstrated that Smb expression is induced by the competence-stimulating peptide (CSP) and that a com box-like sequence is located in the smb promoter region. These results suggest that Smb belongs to the class I bacteriocin family, and its expression is dependent on CSP-induced quorum sensing.

Bacteriocins↗

PubMed1990

Molecular characterization of the gene sr of the saliva interacting protein from Streptococcus mutans OMZ175.

The saliva interacting protein (74KSR) from Streptococcus mutans serotype f, which is immunologically related to antigen I/II from serotype c, also termed B, P1, PAc, is probably involved in the adherence process of Strep. mutans to the tooth surface. A solid-phase adherence assay showed that 38% of the binding of salivary glycoproteins to Strep. mutans OMZ175 was due to this protein. We have cloned and sequenced the 74KSR gene (sr), which produces a recombinant protein (rec195K) with a relative molecular mass of 195,000, as estimated by SDS-PAGE. The strong immunological relationship and functional identity of the 74KSR and rec195K indicate that the Mr 195K protein is probably a precursor form, post-translationally processed, of the 74KSR produced in Strep. mutans. The gene sr consists of 4667 bp and codes for a 171,177 Mr protein. Biochemical features of the protein (density in proline residues and hydrophobicity) may explain the difference observed between the SDS-PAGE estimated molecular mass of the immature protein and the one deduced from the nucleotide sequence. Intra-species hybridization experiments using three contiguous restriction fragments isolated from gene sr as probes showed that the sequence is highly similar in strains from serotypes c and e. We have also shown that a fraction of the heart specific antibodies induced in rabbits during immunization with the 74KSR or rec195K reacts predominantly with human IgG and suggest the hypothesis of antigen mimicry as an explanation for the production of anti-IgG autoantibodies. It will be of great importance to identify the cross-reactive epitopes within the molecule before considering its use in protective immunization against oral streptococci.

Amino Acid Sequence↗

PubMed1979

Wall-associated protein antigens of Streptococcus mutans.

When heat-killed whole organisms of Streptococcus mutans strain Ingbritt (serotype c) were injected into rabbits, antibodies to at least 12 antigens were detectable by crossed immunoelectrophoresis. In contrast, when rabbits were immunized with organisms which had been subjected to extraction with the detergent sodium dodecyl sulphate (SDS), antibodies to only two protein antigens were found. These two proteins (A and B), while existing in a form apparently closely associated with peptidoglycan, could also be recovered from homogenates of whole organisms after sonication and from culture filtrates. Antigenic material was excreted throughout growth. SDS-polyacrylamide gradient gel electrophoresis showed A to have a molecular weight of 29 000, while B had a molecular weight of 190 000. Antigen B was purified to apparent homogeneity as judged by SDS-polyacrylamide gel electrophoresis and isoelectric focusing. All of six strains of serotype c examined produced antigen B. Strains of serotypes e and f also produce antigenically identical proteins and strains of serotypes d and g produce proteins which cross-reacted with antigen B. Antigen B was specifically precipitated by rabbit antiserum to human heart tissue.

Antibody Formation↗

PubMed1983

The influence of ionic strength, pH and a protein layer on the interaction between Streptococcus mutans and glass surfaces.

The initial interaction between Streptococcus mutans and hard surfaces has been investigated using a rotating disc technique. The deposition to clean and BSA-coated glass of two strains of S. mutans, FA-1 (serotype b) and KPSK2 (serotype c), which exhibit different surface properties, was studied. Organisms were harvested from cultures grown in a chemostat at a dilution rate of 0.06 h-1 and suspended in NaCl solutions of defined ionic strengths and pH values. The deposition of both strains showed a strong dependence on electrolyte concentration, particularly at low ionic strengths, which was inversely related to the zeta potentials of the organisms. Similarly, the ionic strength at which maximum deposition was first noted (critical coagulation concentration) for the two strains correlated with their relative potentials. Deposition was insensitive to changes in pH at an electrolyte concentration of 0.05 M. The maximum observed deposition did not approach values predicted by theory, suggesting that a further barrier to deposition, other than electrostatic repulsion, might exist. Under all experimental conditions, some of the deposited bacteria were observed to be oscillating, suggesting that they were held at a distance from the collector surface. The cells did not, however, appear to be deposited in a secondary minimum predicted by DLVO theory hence it may be that long-range polymer interactions are also involved in the deposition of these organisms.

Glass↗

PubMed1999

The immunogenicity of various peptide antigens inducing cross-reacting antibodies to a cell surface protein antigen of Streptococcus mutans.

A cell surface protein antigen (PAc) of Streptococcus mutans may be involved in the binding of bacteria to the tooth surface, and has long been focused upon as a candidate for a preventive vaccine of dental caries. Previously the peptide PAc (365-377) was shown to raise an antibody in B10.D2 mice which inhibited the binding of salivary components to the PAc molecule. Using this peptide as a unit peptide, two constructs based on multiple antigenic peptides, and several types of tandem repeats of two or three copies were synthesized to estimate the immunogenicity of these peptides. Increase in the immunogenicity was observed for all constructs with the use of an adjuvant compared to the unit peptide alone. However, the tandem repeat constructs generally induced antibody production in the absence of adjuvant, while the multiple antigenic peptide constructs did not induce antibody production under the same condition. Although such a phenomenon may be restricted to this particular peptide sequence, these results may influence the strategy for the design of peptide vaccines.

Amino Acid Sequence↗

PubMed2001

Salivary Streptococcus mutans and Lactobacillus sp levels in cardiac children.

This study assesses salivary conditions of 20 children with cardiac disease comparing with a control group of 15 healthy children. The results showed that there was no difference between the groups on salivary flow, buffer capacity and the level of Streptococcus mutans (Sm). The test group i.e., children with cardiac disease, showed a lower level of Lactobacillus sp. The association between the usage of antibiotics and the risk of developing caries, measuring the level of Streptococcus mutans and Lactobacillus sp., showed that children taking antibiotics frequently had a significant lower level of Lactobacillus sp (p<0.05) than healthy children. This association was not found on relation to the levels of Streptococcus mutans.

Adolescent↗

PubMed1976

Regulation and extracellular glucosyltransferase production and the relationship between extracellular and cell-associated activities in Streptococcus mutans.

The regulation of extracellular glucosyltransferase production in Streptococcus mutans GS-5 has been studied using a chemically defined medium. Most of the glucosyltransferase activity produced by cells grown in the chemically defined medium was extracellular, in contrast with the distribution between cell-associated and extracellular glucosyltransferase activity when cells were grown in complex medium. The production of extracellular glucosyltransferase activity coincided with the logarithmic growth phase, and further accumulation ceased when glucose was exhausted from the medium. Accumulation of extracellular glucosyltransferase activity was inhibited immediately by chloramphenicol and rifamycin, added either at the beginning of growth or during mid-logarithmic growth. Low concentrations of chloramphenicol inhibited both cellular protein synthesis and the accumulation of extracellular glucosyltransferase activity to the same extent, indicating a close coupling between glucosyltransferase synthesis and secretion. Experiments using cell lysates showed that no intracellular accumulation of glucosyltransferase activity occurred in the presence of the inhibitors and that the intracellular activity is very low relative to the cell-surface activity. The utilization of cells depleted of cell-associated glucosyltransferase activity indicated that most of the cell-associated glucosyltransferase activity does not act as a precursor for the extracellular enzyme. Sugar analogue inhibitors of glycoprotein synthesis did not have any specific effects on the synthesis or secretion of extracellular glucosyltransferase activity.

Bacterial Proteins↗

PubMed1982

Bacteriolysis of Streptococcus mutans GS5 by lysozyme, proteases, and sodium thiocyanate.

Streptococcus mutans GS5 was grown in a synthetic medium containing radioactive thymidine to monitor cell lysis by assay of the release of DNA. Bacteriolysis was achieved by sequential treatment of the cells with either hen egg white lysozyme and sodium thiocyanate or a combination of hen egg white lysozyme and a proteolytic enzyme followed by addition of the thiocyanate. In the absence of sodium thiocyanate, a small percentage of the total macromolecular thymidine was released in control reaction mixtures during incubation. This amount of released DNA more than doubled in trypsin-treated cells, but the inclusion of lysozyme in reaction mixtures prevented assay of the DNA. Lysis was found to be optimal in the late log phase of growth and was dependent on the concentrations of both lysozyme and protease. Concentrations of trypsin or chymotrypsin as low as 0.01 microgram/ml were found to be effective in enhancing the lytic process. The addition of protease to lysozyme-inorganic salt reaction mixtures altered both the pH and ionic strength profiles of cell lysis. At pHs of 5.5 or lower, both the lysozyme-NaSCN and the lysozyme-trypsin-NaSCN systems were inactive in mediating lysis. The loss of insoluble cell wall peptidoglycan by lysozyme treatment was pH independent and did not appear to be affected by the addition of protease. Either diluted whole saliva or neutrophil extracts could replace trypsin to enhance cell lysis further.

Bacteriolysis↗

PubMed1999

Evidence for the chemical activation of essential cys-302 upon cofactor binding to nonphosphorylating glyceraldehyde 3-phosphate dehydrogenase from Streptococcus mutans.

Nonphosphorylating glyceraldehyde 3-phosphate dehydrogenase (GAPN) from Streptococcus mutans which catalyzes the irreversible oxidation of D-glyceraldehyde-3 phosphate (D-G3P) into 3-phosphoglycerate (3-PGA) in the presence of NADP belongs to the aldehyde dehydrogenase (ALDH) superfamily. Oxidation of D-G3P into 3-PGA by GAPN involves the formation of a covalent enzyme intermediate via the nucleophilic attack of the invariant Cys-302. Titration of Cys-302 in the apo-enzyme by two different kinetic probes, iodoacetamide and 2,2'-dipyridyl disulfide, shows a pK(app) of 8.5 and a chemical reactivity surprisingly low compared to a reactive and accessible thiolate. Binding of NADP causes a strong increase of the reactivity of Cys-302-which is time dependent-with a pK(app) shift from 8.5 to 6.1. Concomitant with the increase in the Cys-302 reactivity, an additional protein fluorescence quenching is observed. These data suggest that cofactor binding induces at least a local conformational rearrangement within the active site. The efficiency of the rearrangement depends on the structure of the cofactors and on the protonation of an amino acid with a pK(app)( )()of 5.7. The rate of the rearrangement also strongly increases when temperature decreases. The data on the conformational rearrangement also reveal an amino acid with a pK(app) of 7.6 whose deprotonation increases the reactivity of the thiolate of Cys-302 by a 3-fold factor. The nature of the amino acid involved-which should be located close to Cys-302 in the holo-active form-is likely the invariant Glu-268. Changing Glu-268 into Ala or Cys-302 into Ala leads to mutants in which the rearrangement is only efficient in the presence of saturating concentrations of both NADP and G3P. The structural aspects of the conformational rearrangement occurring during the catalytic process in the wild-type GAPN should include at least reorientation of both Cys-302 and Glu-268 side chains and repositioning of the nicotinamide ring of the cofactor to permit the chemical activation of Cys-302 and the formation of an efficient ternary complex. Thus, it is likely that the conformation of the active site in the reported X-ray structures of ALDHs determined so far in the presence of cofactor, in which the side chains of Cys-302 and Glu-268 are 6.7 A apart from each other, does not represent the biological active form.

Cysteine↗