Regulation of Streptococcus mutans PTSBio by the transcriptional repressor NigR

Streptococcus mutans is implicated in human dental caries, and the carbohydrate metabolism of this organism plays an important role in the formation of this disease. Carbohydrate transport and metabolism are essential for the survival of S.mutans in the oral cavity. It is known that a unique phosphoenolpyruvate-sugar phosphotransferase system PTSBio of S.mutans UA159 is expressed in sucrose-grown biofilms (Mol Oral Microbiol 28: 2013; 114). In this study we analyzed the transcriptional regulation of the operon (O-Bio) encoding the PTSBio and showed that it was repressed by NigR, a LacI-like transcriptional regulator. Using electro-mobility shift assay, we described two operators to which NigR bound with different affinities. We also identified the transcriptional start site and showed that one of the operators overlaps with the promoter and presumably represses initiation of transcription. Mutational analyses revealed the key nucleotides in the operators required for high-affinity binding of NigR. PTSBio is expressed in S.mutans biofilms so understanding its regulation may provide improved strategies for caries treatment and prevention.