RflM functions as a transcriptional repressor in the autogenous control of the salmonella flagellar master operon flhDC

Abstract

Motility of bacteria like Salmonella enterica is a highly regulated process that responds to a variety of internal and external stimuli. A hierarchy of three promoter classes characterizes the Salmonella flagellar system, and the onset of flagellar gene expression depends on the oligomeric regulatory complex and class 1 gene product FlhD4C2. The flhDC promoter is a target for a broad range of transcriptional regulators that bind within the flhDC promoter region and either negatively or positively regulate flhDC operon transcription. In this work, we demonstrate that the RflM protein is a key component of flhDC regulation. Transposon mutagenesis was performed to investigate a previously described autoinhibitory effect of the flagellar master regulatory complex FlhD4C2. RflM is a LuxR homolog that functions as a flagellar class 1 transcriptional repressor. RflM was found to be the negative regulator of flhDC expression that is responsible for the formerly described autoinhibitory effect of the FlhD4C2 complex on flhDC operon transcription (K. Kutsukake, Mol. Gen. Genet. 254:440-448, 1997). We conclude that upon commencement of flagellar gene expression, the FlhD4C2 complex initiates a regulatory feedback loop by activating rflM gene expression. rflM encodes a transcriptional repressor, RflM, which fine-tunes flhDC expression levels. © 2013, American Society for Microbiology.