Global Transcriptional Analysis of Quorum Sensing-Regulated Genes in Streptococcus mutans

Streptococcus mutans has a conserved quorum-sensing system, called ComCDE. This system is found to regulate diverse physiological processes, including genetic competence, bacteriocin production, biofilm formation and stress response, the key virulence factors in the S. mutans pathogenesis. Objective: To investigate global regulatory mechanism of this system in the virulence expression, we performed a transcriptome analysis to identify quorum sensing-controlled genes of S. mutans. Methods: A S. mutans isogenic mutant, SMDcomC that was unable to produce but still responded to competence-stimulating peptide or CSP, was used for CSP-dependent induction of gene expression under a growth condition with or without CSP (CSP+ or CSP-). Total RNAs were isolated from these groups and purified before used for cDNA synthesis, Cy-dye coupling and array hybridization using an indirect labeling protocol. The S. mutans microarray slides obtained from the Pathogen Functional Genomics Resource Center were scanned with Perkin ScanArray 5000XL Reader. The data were analyzed from TIFF images using TM4 suite software. To validate the array data, qRT-PCR was performed using a SYBR green PCR kit in a Cepheid Smart Cycler. Results: The addition of CSP induced up-regulation of the expression of 150 genes, including bacteriocin-producing and -immunity genes, competence genes, and the genes responsible for DNA repair, stress response and unknown functions. Significant levels of differential gene expression was observed when the cells were grown at the early mid-log phase 15 minutes after addition of CSP. Notably, a number of the genes that were involved in carbohydrate and energy metabolism were up regulated, suggesting that CSP-induced activities required the higher level of energy. We also identified 37 genes that were down regulated or repressed, largely including the genes responsible for protein biosynthesis, transport and unknown functions. Conclusion: The results suggest that the ComCDE quorum sensing system constitutes a unique regulatory pathway to differentially regulate diverse physiological activities of S. mutans.