Transcriptome analysis of Streptococcus mutans biofilm cells deficient in the DpnII restriction-modification system

Human pathogens use cell-cell communication systems, quorum sensing, to regulate virulence factors. Our recent work aiming at deciphering the quorum sensing regulon of Streptococcus mutans, a caries pathogen, revealed a locus encoding an atypical type II restriction-modification (R-M) system, DpnII, comprising two adenine methyltransferases. A recent survey of bacterial genomes demonstrated the widespread occurrence of methylated DNA, and the importance of DNA methylation was highlighted by the diverse processes in which they function. The present study aimed at deciphering the role of DNA methylation during S. mutans biofilm formation. A mutant strain, deficient in the DpnII R-M locus composed of the SMU.504 and SMU.505 genes encoding the two adenine methyltransferases and the SMU.506 gene encoding the DpnII restriction enzyme, was constructed in S. mutans wild-type (WT) strain. Transcriptome analysis was then performed to evaluate the differential biofilm gene expression between the WT cells and the DpnII R-M deficient cells. Overall design: Biofilms were developped in BHI broth complemented with 1% (w/v) sucrose for 6 hours at 37°C in the presence of 5% CO2. The gene expression profiling of the DpnII R-M biofilm mutant cells was compared to the one of the WT biofilm cells.