Regulation of fatty acid biosynthesis by the global regulator CcpA and the local regulator FabT inStreptococcus mutans

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SMU.1745c, encoding a putative transcriptional regulator of the MarR family, maps to a location proximal to thefabgene cluster inStreptococcus mutans. Deletion of the SMU.1745c (fabTSm) coding region resulted in a membrane fatty acid composition comprised of longer-chained, unsaturated fatty acids (UFA), compared with the parent strain. Previous reports have indicated a role for FabT in regulation of genes in thefabgene cluster in other organisms, through binding to a palindromic DNA sequence. Consensus FabT motif sequences were identified inS. mutansin the intergenic regions precedingfabM,fabTSmandfabKin thefabgene cluster. Chloramphenicol acetyltransferase (cat) reporter fusions, using thefabMpromoter, revealed elevated transcription in a ΔfabTSmbackground. Transcription offabTSmwas dramatically elevated in cells grown at pH values of 5 and 7 in the ΔfabTSmbackground. Transcription offabTSmwas also elevated in a strain carrying a deletion for the carbon catabolite repressor CcpA. Purified FabTSmand CcpA bound to the promoter regions offabTSmandfabM. Hence, the data indicate that FabTSmacts as a repressor offabMandfabTSmitself and the global regulator CcpA acts as a repressor forfabTSm.

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