Identification and analysis of flagellar coexpressed determinants (Feds) of Campylobacter jejuni involved in colonization.

The flagellum of Campylobacter jejuni provides motility essential for commensal colonization of the intestinal tract of avian species and infection of humans resulting in diarrhoeal disease. Additionally, the flagellar type III secretion system has been reported to secrete proteins such as CiaI that influence invasion of human intestinal cells and possibly pathogenesis. The flagellar regulatory system ultimately influences σ(28) activity required for expression of the FlaA major flagellin and other flagellar filament proteins. In this work, we discovered that transcription of ciaI and four genes we propose annotating as feds (for flagellar coexpressed determinants) is dependent upon σ(28) , but these genes are not required for motility. Instead, the Feds and CiaI are involved in commensal colonization of chicks, with FedA additionally involved in promoting invasion of human intestinal cells. We also discovered that the major flagellin influences production, stability or secretion of σ(28) -dependent proteins. Specific transcriptional and translational mechanisms affecting CiaI were identified and domains of CiaI were analysed for importance in commensalism or invasion. Our work broadens the genes controlled by the flagellar regulatory system and implicates this system in co-ordinating production of colonization and virulence determinants with flagella, which together are required for optimal interactions with diverse hosts.