A small protein essential for flagellar assembly and virulence of Campylobacter jejuni

Campylobacter jejuni is the leading cause of bacterial food-poisoning, with motility being an essential virulence factor. While many aspects of flagella biogenesis have been studied, a complete picture of the components and regulators of these multi-protein machines is still missing. To identify genes crucial for C. jejuni pathogenesis and motility, we applied transposon sequencing in a humanized tissue model. This revealed three largely uncharacterized genes (pflC , pflD , pflE ) as essential for motility. While PflC/D turned out to be components of the flagellar motor disk structures, PflE is a small protein of only 57 aa. PflE strikingly affects motor biogenesis, with complete loss of motor structures upon its deletion. We demonstrate PflE is a lipoprotein and supports outer-membrane localization of the main basal-disk protein FlgP. With motility as a critical Campylobacter virulence factor, our work demonstrates that deletion of a small protein can bring a bacterial pathogen to a halt.