Unbalanced growth and macromolecular synthesis in Streptococcus mutans FA-1

Streptococcus mutans gene expression and functional profile in root caries: an RNA-seq study

The literature is still scarce on studies describing S. mutans global gene expression under clinical conditions such as those found on complex biofilms from sound root surfaces (SRS) and carious root surfaces (RC). This study aimed to investigate the S. mutans gene expression and functional profile within the metatranscriptome of biofilms from SRS and from RC in an attempt to identify enriched functional signatures potentially associated with healthy to disease transitioning process. Total RNA was extracted, and prepared libraries (SRS=10 and RC=9) were paired-end sequenced using the Illumina HiSeq2500. Read count assigned to each gene of the S. mutans UA159 strain were obtained. Differentially expressed genes (DEG) between SRS and RC were identified using the DESeq2 R package and weighted gene co-expression network analysis (WGCNA) was performed to explore and identify functional modules related to SRS and RC. We found seventeen DEG between SRS and RC samples, with three overexpressed in RC and related to membrane protein, alanyl-tRNA synthetase and GTP-binding protein with the remaining ones overexpressed in SRS samples and related to hypothetical protein, transposon integrase, histidine kinase, putative transporter, bacteriocin immunity protein, response regulator, 6-phospho-beta-galactosidase, purine metabolism and to transcriptional regulator. Key-functional modules were identified for SRS and RC conditions based on WCGNA, being 139 hub genes found on SRS key-module and 17 genes on RC key-module. Functional analysis of S. mutans within the metatranscriptome of biofilms from sound root and from carious root revealed a similar pattern of gene expression, and only a few genes have been differentially expressed between biofilms from sound root surfaces and from root carious lesions. However, S. mutans presented a greater functional abundance in the lesion samples. Some functional patterns related to sugar (starch, sucrose, fructose, mannose and lactose) and heterofermentative metabolisms, to cell-wall biosynthesis and to acid tolerance stress seem to be enriched on carious root surfaces conferring ecological advantages to S. mutans. Altogether, the present data suggest that a functional signature may be associated with carious root lesions.

Changes in transcript abundance in Chlamydomonas reinhardtii following nitrogen deprivation predict diversion of metabolism

Like many microalgae, Chlamydomonas reinhardtii forms lipid droplets rich in triacylglycerols when nutrient deprived. To begin studying the mechanisms underlying this process, nitrogen (N) deprivation was used to induce triacylglycerol accumulation and changes in developmental programs such as gametogenesis. Comparative global analysis of transcripts under induced and noninduced conditions was applied as a first approach to studying molecular changes that promote or accompany triacylglycerol accumulation in cells encountering a new nutrient environment. Towards this goal, high-throughput sequencing technology was employed to generate large numbers of expressed sequence tags of eight biologically independent libraries, four for each condition, N replete and N deprived, allowing a statistically sound comparison of expression levels under the two tested conditions. As expected, N deprivation activated a subset of control genes involved in gametogenesis while down-regulating protein biosynthesis. Genes for components of photosynthesis were also down-regulated, with the exception of the PSBS gene. N deprivation led to a marked redirection of metabolism: the primary carbon source, acetate, was no longer converted to cell building blocks by the glyoxylate cycle and gluconeogenesis but funneled directly into fatty acid biosynthesis. Additional fatty acids may be produced by membrane remodeling, a process that is suggested by the changes observed in transcript abundance of putative lipase genes. Inferences on metabolism based on transcriptional analysis are indirect, but biochemical experiments supported some of these deductions. The data provided here represent a rich source for the exploration of the mechanism of oil accumulation in microalgae.

Mechanism of penicillin killing in the absence of bacterial lysis

Exposure of group A streptococci (a nonlytic-death phenotype) to benzylpenicillin (penicillin G) produced a dose-dependent, rapid, and extensive hydrolysis of total cellular RNA, with the subsequent loss of hydrolysis products from the cell. This loss of RNA correlated well with loss of viability and was not accompanied by solubilization of the cell wall or comparable losses of either protein or DNA. Simultaneous treatment with penicillin G and either chloramphenicol or rifampin resulted in reduced levels of killing and the complete inhibition of RNA loss. These findings define a new mechanism of penicillin G-induced killing in the absence of cell wall disruption and suggest a basis for drug-induced antagonism of penicillin G-mediated nonlytic death.

Abnormal form of Aspergillus terreus isolated from mycotic abscesses

A remarkable outer cell-wall thickening (up to 1.5 muM) was observed on septate hyphae obtained from pus collected from multiple abscesses of a 25-year-old female patient. Ultrastructural examination of the hyphae showed a thick electron dense layer of microfibrillar material surrounding the electron transparent cell wall. The organism was able to grow only on hypertonic media upon initial isolation but on later subculture it grew on normal isotonic media. The thick microfibrillar material diminished progressively upon subculture but could be demonstrated in 7 day secondary cultures in isotonic liquid medium. There, microfibrillar bridges appeared to bind hyphae together. The observations suggested that this microfibrillar material was a true extracellular component. The immunological status of the patient was not examined, but her 10 year history of multiple mycotic abscesses and dermatophytoses suggested some abnormalities.

Effects of mecillinam and cefoxitin on growth, macromolecular synthesis, and penicillin-binding proteins in a variety of streptococci

Although some strains of streptococci seem to be virtually inert to mecillinam, the growth of other strains, notably certain viridans streptococci (Streptococcus mutans and Streptococcus sanguis) was inhibited by relatively low concentrations of the drug. Inhibition of the synthesis of peptidoglycan, RNA, protein, and DNA in two tolerant strains, S. mutans FA-1 and GS-5, was studied over a wide range of concentrations of mecillinam, benzylpenicillin, and cefoxitin. The responses of both strains to all three beta-lactams were very similar; that is, synthesis of insoluble peptidoglycan was most susceptible. Inhibition of peptidoglycan synthesis was followed rapidly and sequentially by substantial but less severe inhibitions of RNA and protein synthesis. Significant inhibition of DNA synthesis was not observed. Binding studies with [14C]benzylpenicillin alone or after preexposure of membrane preparations to benzylpenicillin, mecillinam, or cefoxitin suggest that reasonably selective binding of a beta-lactam antibiotic to one or two of the major penicillin-binding proteins (PBP 1 or PBP 4) of S. mutans GS-5 and FA-1 may be the initial step in the series of events that results in the inhibition of growth and in the inhibition of insoluble peptidoglycan assembly and of RNA and protein synthesis.

Biology, immunology, and cariogenicity of Streptococcus mutans

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Conservation of cell wall peptidoglycan by strains of Streptococcus mutans and Streptococcus sanguis

Turnover of the cell wall peptidoglycan fraction of six different strains of Streptococcus mutans and eight different strains of Streptococcus sanguis was examined. Cells were grown in the presence of [3H]lysine and [14C]leucine for at least eight generations and then chased in growth medium lacking the two labels. At intervals during the chase, samples of cultures were removed, and the amounts of the two labeled precursors remaining in the peptidoglycan and protein fractions were quantitated. Similar experiments were done in which the pulse-labeling technique was used. In addition, cells were labeled in the presence of tetracycline or penicillin, chased with growth medium containing no inhibitor, and assayed at intervals during the chase for the amount of [3H]lysine present in peptidoglycan fractions. Studies of cultures of S. mutans strains FA-1, OMZ-61, OMZ-176, 6715, GS-5, and Ingbritt and of S. sanguis strains 10558, M-5, Wicky, DL-101, DL-1, 71X26, and 71X48 maintained in the exponential phase of growth in a chemically defined medium failed to show evidence of loss of insoluble peptidoglycan via turnover. Similarly, for the strains of S. mutans, insoluble peptidoglycan assembled during 2 h of benzylpenicillin or tetracycline treatment was also conserved during recovery from growth inhibition.

Inhibition of peptidoglycan, ribonucleic acid, and protein synthesis in tolerant strains of Streptococcus mutans

Exposure of exponentially growing cultures of Streptococcus mutans strains FA-1 and GS-5 to various concentrations of benzylpenicillin (Pen G) resulted in inhibition of turbidity increases at low concentrations (0.02 to 0.04 mug/ml). However, in contrast to some other streptococcal species, growth inhibition was not accompanied by cellular lysis or by a rapid loss of viability. In both strains, synthesis of insoluble cell wall peptidoglycan was very sensitive to Pen G inhibition and responded in a dose-dependent manner to concentrations of about 0.2 and 0.5 mug/ml for strains GS-5 and FA-1, respectively. Higher Pen G concentrations failed to inhibit further either growth or insoluble peptidoglycan assembly. Somewhat surprisingly, Pen G also inhibited both ribonucleic acid (RNA) and protein syntheses, each in a dose-dependent manner. Compared with inhibition of peptidoglycan synthesis, inhibition of RNA and protein syntheses by Pen G was less rapid and less extensive. Maximum amounts of radiolabeled Pen G were specifically bound to intact cells upon exposure to about 0.2 and 0.5 mug/ml of Pen G for strains GS-5 and FA-1, respectively, concentrations consistent with those that resulted in maximum or near-maximum inhibitions of the synthesis of cellular peptidoglycan, RNA, and protein. Five polypeptide bands that had a very high affinity for [(14)C]Pen G were detected in a crude cell envelope preparation of strain FA-1. After exposure of cultures of strain FA-1 to the effects of saturating concentrations of the drug for up to 3 h, addition of penicillinase was followed by recovery of growth after a lag. The length of the lag before regrowth depended on both Pen G concentration and time of exposure. On the basis of these and other observations, it is proposed that the secondary inhibitions of cellular RNA or protein synthesis, or both, are involved in the tolerance of these organisms to lysis and killing by Pen G and other inhibitors of insoluble peptidoglycan assembly.

Protein-to-wet weight relationships in supragingival plaques from caries-prone tooth surfaces

The ratio of protein to wet weight in unpooled samples of supragingival plaques from sound and carious tooth surfaces was studied. Protein was assayed by a procedure developed for the study, in order to achieve a sensitivity of 1 microgram with minimum effects upon quantitation from protein composition and nonprotein components. Ratios of protein to wet weight in plaque specimens from caries-free surfaces were almost equally distributed into two main categories of 9.4% and 6.5%. Corresponding values for specimens from carious surfaces were 9.1% and 5.0%. The occurrence of high and of low values among samples from each type of surface indicated that the plaques differed quantitatively in protein, water, or a nonprotein component, possibly extracellular polysaccharide. Although compositional differences between plaques from the two types of surfaces were indicated by the lower ratios of 6.5% from noncarious and 5.0% from carious surfaces, they were not indicated by the higher ratio values, which were similar. These results suggest either that protein-to-wet weight ratios are not related to caries, or that the ratio values are related to caries for some but not all types of plaques.

Electron microscopy and immunoperoxidase staining of Streptococcus mutans during controlled growth in two different media

Streptococcus mutans subspecies sobrinus serotype d (B13) was cultivated in a fermentor under controlled conditions in two different media: a complex proteose-peptone medium and a defined minimal medium (C4). Specimens from different growth phases were examined by electron-microscopy and tested electron-immunohistochemically. Irrespective of the growth medium used, no differences were observed in the immunohistochemical staining pattern of bacteria during the lag, the exponential and the early staionary phases. Specimens obtained several hours after exponential growth contained areas where the bacteria showed staining that ranged from a strong deposit of reaction product to no deposit. This appearance seems partly to explain the differences in the intensity of immunohistochemical staining of certain bacteria observed in dental plaques stained for identification of S. mutans subspecies sorbrinus.

Recovery of Streptococcus mutans after amino acid deprivation

The recovery of Streptococcus mutans FA-1 in a complete, chemically defined medium was examined after 1, 3, and 6 h of essential amino acid deprivation. Amino acids could be divided into two groups based on their effect on the relative rates of recovery: those amino acids (leucine and cystine) that are precursors of protein only, and amino acids (glutamate/glutamine or lysine) that are incorporated into both protein and cell wall peptidoglycan. Culture turbidity, deoxyribonucleic acid, ribonucleic acid, protein and cell wall peptidoglycan measurements indicated rapid recovery after leucine/cystine starvation periods. However, a 6-h leucine/cystine deprivation resulted in a slower exponential rate of growth (180-min doubling time compared to the normal doubling time of 85 to 90 min) after recovery. Glutamate/glutamine starvation, on the contrary, resulted in greatly extended recovery periods, especially after 3- and 6-h amino acid deprivations. Macromolecular synthesis was most severely affected by 6-h glutamate/glutamine starvation and required 6 to 10 h for recovery of an exponential rate. A delay in the recovery of deoxyribonucleic acid and cell wall peptidoglycan synthesis beyond that of the other macromolecules was observed after 1 and 3 h of deprivation with either leucine/cystine or glutamate/glutamine. However, after a 6-h amino acid deprivation, deoxyribonucleic acid synthesis recovered more rapidly than that of the other macromolecules studied. The results are discussed in terms of the nutritional environment of the oral cavity and its effect on the growth and survival of S. mutans.

Factors regulating cell wall thickening and intracellular iodophilic polysaccharide storage in Streptococcus mutans

The effects of a series of different antibiotics on the synthesis and accumulation of deoxyribonucleic acid (DNA), ribonucleic acid (RNA), protein, cell wall peptidoglycan (PG), and intracellular iodophilic polysaccharide (IPS) in Streptococcus mutans FA-1 were examined. d-Cycloserine, penicillin G, or vancomycin treatment resulted in rapid inhibitions of PG synthesis and a consequent decrease in the relative amount of lysine found in PG fractions. Decreases in culture turbidity, an indicator of gross cellular lysis, were not observed. Secondary inhibitions of the rates and extent of syntheses of DNA, RNA, and protein were observed. With all three inhibitors of PG synthesis, IPS synthesis continued for varying time intervals but, at most, resulted in only relatively small and transient increases in cellular IPS content. Chloramphenicol inhibited protein synthesis but permitted continued synthesis of RNA and PG. After 6 h, the cells contained 42% of their [(3)H] lysine in the PG fraction compared with 25% in exponential-phase cells, a good indication of thickened cell walls. In the presence of chloramphenicol, cellular IPS content increased about 2.5-fold during the first 45 min and then decreased to a level (13%) at 6 h very similar to that of exponential-phase cells (about 10%). Rifampin inhibition of RNA (and, consequently, also protein) synthesis resulted in accumulation of cellular PG and IPS. After 6 h, IPS accounted for 38% of the cellular dry weight, and the cells contained 43% of their lysine in PG. Thus, rifampin-inhibited cells appear to have both thickened walls and a high IPS content. The correlation between inhibition of RNA synthesis and IPS accumulation was confirmed by exposing cultures to rifampin for 60 min and then removing the drug, thus permitting the cells to regrow. Upon removal of rifampin and resumption of RNA synthesis, cellular IPS content rapidly decreased to the level expected for exponentialphase cells.