Streptococcus mutans is a normal resident of dental plaque that metabolizes sugars to acid that can demineralize tooth enamel, thereby causing dental caries. S. mutans uses a signal peptide-histidine kinase-response regulator system, the components of which are encoded by the comC, comD and comE genes, respectively. These genes play a role in genetic competence, biofilm formation and acid tolerance. From previous proteomic and bioinformatic analyses, a large set of genes were predicted to be differentially expressed by the activation of the ComCDE system. Objectives: To identify genes whose expressions are controlled by the ComCDE system using differential display PCR (dd-PCR). Using a comC deletion mutant which does not produce endogenous competence-stimulating peptide (CSP), we attempted to detect the altered expression of genes during competence development. Methods: S. mutans comC mutant strain SMCC1 was grown in selective THYE media and treated with synthetic CSP for 10, 20 or 30 minutes. Total RNA was isolated from untreated and treated samples, subjected to RT-PCR, digested with restriction enzyme, ligated with adaptors and amplified using ³³P radiolabelled primers. The amplification products were resolved in a 7% denaturing polyacrylamide gel, dried and autoradiographed. Fragments showing differential expressions were excised from the gel, reamplified, and cloned into pPCR-Script for sequencing. Results: Forty gene fragments were found to be up-regulated, while 36 were found to be down-regulated. Forty-two fragments were differentially expressed in other patterns.Conclusions: The altered expression of numerous S. mutans genes in response to CSP was detectable by dd-PCR. Supported by Grant RO1 DE013230 from the National Institutes of Health and grant MT-15431 from the Canadian Institutes of Health Research.

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