Role of Streptococcus mutans surface proteins for biofilm formation

Abstract

Streptococcus mutans has been implicated as a primary causative agent of dental caries in humans. An important virulence property of the bacterium is its ability to form biofilm known as dental plaque on tooth surfaces. In addition, this organism also produces glucosyltransferases, multiple glucan-binding proteins, protein antigen c, and collagen-binding protein, surface proteins that coordinate to produce dental plaque, thus inducing dental caries. Bacteria utilize quorum-sensing systems to modulate environmental stress responses. A major mechanism of response to signals is represented by the so called two-component signal transduction system, which enables bacteria to regulate their gene expression and coordinate activities in response to environmental stress. As for S. mutans, a signal peptide-mediated quorum-sensing system encoded by comCDE has been found to be a regulatory system that responds to cell density and certain environmental stresses by excreting a peptide signal molecule termed CSP (competence-stimulating peptide). One of its principal virulence factors is production of bacteriocins (peptide antibiotics) referred to as mutacins. Two-component signal transduction systems are commonly utilized by bacteria to regulate bacteriocin gene expression and are also related to biofilm formation by S. mutans.

Keywords: Biofilm; Signal transduction; Streptococcus mutans; Surface proteins.

Figure 1

Representative confocal images of bacterial cells (green) and glucans (red) within biofilm formed by S. mutans MT8148 on tooth enamel surface in presence of 0.5% (wt/vol) sucrose.

Figure 2

Biofilm analysis using confocal laser scanning microscopy. (A) Representative three-dimensional images of biofilms formed by S. mutans MT8148 (a) and AD1 (b) in the presence of 0.5% sucrose. (B) x–z section and z-projection of biofilm formed by MT8148 (c) and AD1 (d). S. mutans was stained with SYTO^®9 green fluorescent nucleic acid stain (green) and labeled-dextran (Alexa Fluor^® 647; red) was used.

Figure 3

Results of NCBI Conserved Domains Database search of loop regions relative to the putative dextran-binding domain in GbpC. (A) Glucan-binding protein C: S. mutans. (B) Glucan binding protein C: S. macacae. (C) AgiII: S. mutans. (D) SpaA: S. sobrinus. (E) Probable cell-surface antigen I/II: S. intermedius. Asterisks indicate mid-points. Bold letters indicate core regions of potential dextran-binding domain sequences. Lower-case letters indicate no homology among strains.