Vibrio cholerae has a single polar sheathed flagellum that propels the cells of this bacterium. Flagellar synthesis, motility, and chemotaxis have all been linked to virulence in this human pathogen. V. cholerae expresses flagellar genes in a hierarchy consisting of σ54- and σ28-dependent transcription. In other bacteria, σ28 transcriptional activity is controlled by an anti-σ28 factor, FlgM. We demonstrate that the V. cholerae FlgM homologue (i) physically interacts with σ28, (ii) has a repressive effect on some V. cholerae σ28-dependent flagellar promoters, and (iii) is secreted through the polar sheathed flagellum, consistent with anti-σ28 activity. Interestingly, FlgM does not have a uniform repressive effect on all σ28-dependent promoters, as determined by measurement of σ28-dependent transcription in cells either lacking FlgM (Δflg]M or incapable of secretion (ΔfliF). Further analysis of a ΔfliF strain revealed that this flagellar assembly block causes a decrease in class III (FlrC- and σ54-dependent) and class II (FlrA-dependent), but not class II (FlrA- and σ54- dependent), flagellar transcription. V. cholerae flgM and fliA (encodes σ28) mutants were only modestly affected in their ability to colonize the infant mouse intestine, a measure of virulence. Our results demonstrate that V. cholerae FlgM functions as an anti-σ28 factor and that the sheathed flagellum is competent for secretion of nonstructural proteins.
ASJC Scopus subject areas
- Molecular Biology