Transcriptional regulation of cpsQ‐mfpABC and mfpABC by CalR in Vibrio parahaemolyticus

The cpsQ‐mfpABC locus is transcribed as two operons, i.e., cpsQ‐mfpABC and mfpABC, in Vibrio parahaemolyticus, and both of them are all required for biofilm formation. CalR belongs to the LysR‐type transcriptional regulator family, and was originally identified as a repressor of the swarming motility and T3SS1 genes expression in V. parahaemolyticus. In the present work, a combination of qRT‐PCR, primer extension, LacZ fusion expression, electrophoretic mobility shift assay, and DNase I footprinting assays were employed to elucidate the regulatory mechanisms of cpsQ‐mfpABC and mfpABC by CalR. One transcription start site for each operon was detected and their activities were activated by CalR. His‐CalR protected two DNA regions upstream of mfpABC against DNase I digestion, but no binding sites were detected in the promoter region of cpsQ‐mfpABC, suggesting a direct and an indirect regulatory manner for mfpABC and cpsQ‐mfpABC transcription by CalR, respectively. Collectively, the results presented here confirmed a new physiological role for CalR that acts as an activator for cpsQ‐mfpABC and mfpABC transcription.