scholarly journals Cell Density Modulates Acid Adaptation in Streptococcus mutans: Implications for Survival in Biofilms

2001 ◽  
Vol 183 (23) ◽  
pp. 6875-6884 ◽  
Author(s):  
Yung-Hua Li ◽  
Michael N. Hanna ◽  
Gunnel Svensäter ◽  
Richard P. Ellen ◽  
Dennis G. Cvitkovitch
Keyword(s):  
Streptococcus Mutans ◽  
Cell Density ◽  
Culture Filtrate ◽  
High Cell Density ◽  
Acid Tolerance ◽  
Low Ph ◽  
Growth Mode ◽  
High Cell ◽  
Biofilm Growth ◽  
Acid Adaptation

ABSTRACT Streptococcus mutans normally colonizes dental biofilms and is regularly exposed to continual cycles of acidic pH during ingestion of fermentable dietary carbohydrates. The ability ofS. mutans to survive at low pH is an important virulence factor in the pathogenesis of dental caries. Despite a few studies of the acid adaptation mechanism of this organism, little work has focused on the acid tolerance of S. mutans growing in high-cell-density biofilms. It is unknown whether biofilm growth mode or high cell density affects acid adaptation by S. mutans. This study was initiated to examine the acid tolerance response (ATR) of S. mutans biofilm cells and to determine the effect of cell density on the induction of acid adaptation. S. mutans BM71 cells were first grown in broth cultures to examine acid adaptation associated with growth phase, cell density, carbon starvation, and induction by culture filtrates. The cells were also grown in a chemostat-based biofilm fermentor for biofilm formation. Adaptation of biofilm cells to low pH was established in the chemostat by the acid generated from excess glucose metabolism, followed by a pH 3.5 acid shock for 3 h. Both biofilm and planktonic cells were removed to assay percentages of survival. The results showed that S. mutans BM71 exhibited a log-phase ATR induced by low pH and a stationary-phase acid resistance induced by carbon starvation. Cell density was found to modulate acid adaptation in S. mutans log-phase cells, since pre-adapted cells at a higher cell density or from a dense biofilm displayed significantly higher resistance to the killing pH than the cells at a lower cell density. The log-phase ATR could also be induced by a neutralized culture filtrate collected from a low-pH culture, suggesting that the culture filtrate contained an extracellular induction component(s) involved in acid adaptation in S. mutans. Heat or proteinase treatment abolished the induction by the culture filtrate. The results also showed that mutants defective in thecomC, -D, or -E genes, which encode a quorum sensing system essential for cell density-dependent induction of genetic competence, had a diminished log-phase ATR. Addition of synthetic competence stimulating peptide (CSP) to the comC mutant restored the ATR. This study demonstrated that cell density and biofilm growth mode modulated acid adaptation in S. mutans, suggesting that optimal development of acid adaptation in this organism involves both low pH induction and cell-cell communication.

scholarly journals Genetic characterization of the hdrRM operon: a novel high-cell-density-responsive regulator in Streptococcus mutans

Microbiology ◽  
2007 ◽  
Vol 153 (8) ◽  
pp. 2765-2773 ◽  
Author(s):  
Justin Merritt ◽  
Lanyan Zheng ◽  
Wenyuan Shi ◽  
Fengxia Qi
Keyword(s):  
Streptococcus Mutans ◽  
Cell Density ◽  
Genetic Characterization ◽  
High Cell Density ◽  
High Cell

scholarly journals pH AND POPULATION DENSITY IN THE REGULATION OF ANIMAL CELL MULTIPLICATION

1971 ◽  
Vol 51 (3) ◽  
pp. 686-702 ◽  
Author(s):  
H. Rubin
Keyword(s):  
Cell Migration ◽  
Cell Density ◽  
Plasma Membranes ◽  
High Cell Density ◽  
Low Ph ◽  
Cell Multiplication ◽  
High Cell ◽  
High Ph ◽  
Cell Densities ◽  
Very High

Sparse and dense cultures of chick embryo cells were affected differently by pH. The rates of cell multiplication and of thymidine-3H incorporation into DNA of dense cultures were increased as the pH was increased from 6.6 to 7.6. At pH higher than 7.6 the rate of multiplication decreased slightly in the dense cultures, but the rate of thymidine-3H incorporation continued to increase. The discrepancy was due in part to cell death and detachment at very high pH, and in part to a more rapid uptake of thymidine-3H at very high pH. Sparse cultures were much less sensitive to pH reduction and, when a suitably conditioned medium was used to minimize cell damage, very sparse cultures grew almost as well at pH 6.7 as at higher pH. The rates of cell multiplication and thymidine-3H incorporation at low pH decreased in the initially sparse cultures before they reached confluent cell densities. There was no microscope evidence of direct contact between plasma membranes of cells at these densities although the parallel orientation indicated that the cells were influencing locally each other's behavior. Even at much higher cell densities, electron microscopy revealed large intercellular gaps partly filled with a fragmentary electron-opaque material suspected to be glycoprotein. Wounding experiments showed that pH affected cell migration in a manner similar to its effects on cell multiplication. Low pH inhibited cell migration, but those cells which migrated into the denuded region multiplied as rapidly at low pH as at high pH. The effects of pH on growth were correlated with effects on the uptake of 2-deoxyglucose-3H. Dense populations of cells inhibited by low pH were stimulated to incorporate thymidine-3H by the addition of small amounts of diethylaminoethyl-dextran. Rous sarcoma cells at high cell density were less sensitive to pH than were normal cells at the same density, but were more sensitive than sparse normal cultures. The results suggest that cell growth is inhibited through the combined effects of both lowered pH and high cell density on cell surface permeability.

scholarly journals Regulation of Bacteriocin Production in Streptococcus mutans by the Quorum-Sensing System Required for Development of Genetic Competence

2005 ◽  
Vol 187 (12) ◽  
pp. 3980-3989 ◽  
Author(s):  
Jan R. van der Ploeg
Keyword(s):  
Streptococcus Mutans ◽  
Cell Density ◽  
High Cell Density ◽  
Regulatory System ◽  
Bacteriocin Production ◽  
Repeat Element ◽  
High Cell ◽  
Gene Encoding ◽  
Immunity Protein ◽  
Genes Encoding

ABSTRACT In Streptococcus mutans, competence for genetic transformation and biofilm formation are dependent on the two-component signal transduction system ComDE together with the inducer peptide pheromone competence-stimulating peptide (CSP) (encoded by comC). Here, it is shown that the same system is also required for expression of the nlmAB genes, which encode a two-peptide nonlantibiotic bacteriocin. Expression from a transcriptional nlmAB′-lacZ fusion was highest at high cell density and was increased up to 60-fold following addition of CSP, but it was abolished when the comDE genes were interrupted. Two more genes, encoding another putative bacteriocin and a putative bacteriocin immunity protein, were also regulated by this system. The regions upstream of these genes and of two further putative bacteriocin-encoding genes and a gene encoding a putative bacteriocin immunity protein contained a conserved 9-bp repeat element just upstream of the transcription start, which suggests that expression of these genes is also dependent on the ComCDE regulatory system. Mutations in the repeat element of the nlmAB promoter region led to a decrease in CSP-dependent expression of nlmAB′-lacZ. In agreement with these results, a comDE mutant and mutants unable to synthesize or export CSP did not produce bacteriocins. It is speculated that, at high cell density, bacteriocin production is induced to liberate DNA from competing streptococci.

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