Loss of a Cardiolipin Synthase in G27 Blocks Flagellum Assembly.

uses a cluster of polar, sheathed flagella for motility, which it requires for colonization of the gastric epithelium in humans. As part of a study to identify factors that contribute to localization of the flagella to the cell pole, we disrupted a gene encoding a cardiolipin synthase () in strains G27 and B128. Flagellum biosynthesis was abolished in the G27 mutant but not in the B128 mutant. Transcriptome sequencing analysis showed that flagellar genes encoding proteins needed early in flagellum assembly were expressed at wild-type levels in the G27 mutant. Examination of the G27 mutant by cryo-electron tomography indicated the mutant assembled nascent flagella that contained the MS ring, C ring, flagellar protein export apparatus, and proximal rod. Motile variants of the G27 mutant were isolated after allelic exchange mutagenesis using genomic DNA from the B128 mutant as the donor. Genome resequencing of seven motile G27 recipients revealed that each isolate contained the (encodes the P-ring protein) allele from B128. Replacing the allele in the G27 mutant with the B128 allele rescued flagellum biosynthesis. We postulate that G27 FlgI fails to form the P ring when cardiolipin levels in the cell envelope are low, which blocks flagellum assembly at this point. In contrast, B128 FlgI can form the P ring when cardiolipin levels are low and allows for the biosynthesis of mature flagella. colonizes the epithelial layer of the human stomach, where it can cause a variety of diseases, including chronic gastritis, peptic ulcer disease, and gastric cancer. To colonize the stomach, must penetrate the viscous mucous layer lining the stomach, which it accomplishes using its flagella. The significance of our research is identifying factors that affect the biosynthesis and assembly of the flagellum, which will contribute to our understanding of motility in , as well as other bacterial pathogens that use their flagella for host colonization.