Liw controls growth-phase expression of campylobacter jejuni flagellar and non-flagellar proteins via the post-transcriptional regulator CsrA

Campylobacter jejuni is an important human pathogen that causes 96 million cases of acute diarrheal disease worldwide each year. We have shown that C. jejuni CsrA is involved in the post-transcriptional regulation of more than 100 proteins, and altered expression of these proteins is presumably involved in the altered virulence-related phenotypes of a csrA mutant. Mutation of fliW results in C. jejuni cells that have greatly truncated flagella, are less motile, less able to form biofilms, and exhibit a reduced ability to colonize chicks. The loss of FliW results in the altered expression of 153 flagellar and non-flagellar proteins, the majority of which are members of the CsrA regulon. The number of proteins dysregulated in the fliW mutant was greater at mid-log phase (120 proteins) than at stationary phase (85 proteins); 52 proteins showed altered expression at both growth phases. Loss of FliW altered the growth-phase- and CsrA-mediated regulation of FlaA flagellin. FliW exerts these effects by binding to both FlaA and to CsrA, as evidenced by pull-down assays, protein-protein cross-linking, and size-exclusion chromatography. Taken together, these results show that CsrA-mediated regulation of both flagellar and non-flagellar proteins is modulated by direct binding of CsrA to the flagellar chaperone FliW. Changing FliW:CsrA stoichiometries at different growth phases allow C. jejuni to couple the expression of flagellar motility to metabolic and virulence characteristics.