H-NS represses fliD transcription for lateral flagellar filament cap in Vibrio parahaemolyticus

Vibrio parahaemolyticus propels itself through liquids using a polar flagellum and efficiently swarms across surfaces or viscous environments with the aid of lateral flagella. H-NS plays a negative role in the swarming motility of V. parahaemolyticus by directly repressing the transcription of the lateral flagellin gene lafA. However, it remains unknown whether H-NS can directly regulate other lateral flagellar genes in V. parahaemolyticus. In this study, we investigated the regulation of fliD, which is responsible for the lateral flagellar filament cap, by H-NS using quantitative real-time PCR, luminescence assay, two-plasmid lacZ fusion assay, electrophoretic mobility shift assay, and DNase I footprinting assay. We found that H-NS represses the transcription of fliD. Overexpression of H-NS in Escherichia coli resulted in the repression of the promoter activity of fliD. Furthermore, His-tagged H-NS was shown to protect a specific DNA region located 11 to 188 base pairs upstream of fliD from DNase I digestion. Therefore, it can be concluded that H-NS directly and negatively regulates the transcription of fliD. This study has contributed to our understanding of the regulatory mechanisms of H-NS on lateral flagella-propelled swarming motility in V. parahaemolyticus.