Secretion of Virulence Proteins from Campylobacter jejuni Is Dependenton a Functional Flagellar Export Apparatus

Campylobacter jejuni, a gram-negative motile bacterium, secretes a set of proteins termed the Campylobacter invasion antigens (C ia proteins). The purpose of this study was to determine whether the flagellar apparatus serves as the export apparatus for the Cia proteins. M utations were generated in five genes encoding three structural components of the flagella, the flagellar basal body (JigB and flgC ), hook (JigE2)，and filament (flaA and flaB ) genes, as well as in genes whose products are essential for flagellar protein export (JlhB and flil). W hile mutations that affected filament assembly were found to be nonmotile (Mot^- ) and did not secrete Cia proteins (S^-), a flaA iflaB⁺) filament mutant was found to be nonmotile but Cia protein secretion competent(Mot^-, S⁺). Complementation of a flaA flaB double mutant with a shuttle plasmid harboring either the flaA or flaB gene restored Cia protein secretion, suggesting that Cia export requires at least one of the two filament proteins. Infection of INT 407 human intestinal cells with the C. jejuni mutants revealed that maximal invasion of the epithelial cells required motile bacteria that are secretion competent. Collectively, these data suggest that the C. jejuni Cia proteins are secreted from the flagellar export apparatus.