Summary The helical shape of the human stomach pathogen Helicobacter pylori has been suggested to provide mechanical advantage for penetrating the viscous stomach mucus layer. Using single-cell tracking and quantitative morphology analysis we document marked variation in cell body helical parameters and flagellum number among H. pylori strains leading to distinct and broad speed distributions in broth and viscous gastric mucin media. These distributions reflect both temporal variation in swimming speed and morphologic variation within the population. Isogenic mutants with straight-rod morphology showed 7–21% reduction in speed and a lower fraction of motile bacteria. Mutational perturbation of flagellum number revealed a 19% increase in speed with 4 vs. 3 median flagellum number. Resistive force theory modeling incorporating variation of both cell shape and flagellum number predicts qualitative speed differences of 10–30% among strains. However, quantitative comparisons suggest RFT underestimates the influence of cell body shape on speed for helical shaped bacteria.

Flagellar biogenesis in the gastric pathogen Helicobacter pylori involves a transcriptional hierarchy that utilizes all three sigma factors found in this bacterium (RpoD, RpoN and FliA). Transcription of the RpoN-dependent genes requires the sensor kinase FlgS and response regulator FlgR. It is thought that FlgS senses some cellular cue to regulate transcription of the RpoN-dependent flagellar genes, but this signal has yet to be identified. Previous studies showed that transcription of the RpoN-dependent genes is inhibited by mutations in flhA, which encodes a membrane-bound component of the flagellar protein export apparatus. We found that depending on the H. pylori strain used, insertion mutations in flhA had different effects on expression of RpoN-dependent genes. Mutations in flhA in H. pylori strains B128 and ATCC 43504 (the type strain) were generated by inserting a chloramphenicol resistance cassette so as to effectively eliminate expression of the gene (DflhA), or within the gene following codon 77 (designated flhA77) or codon 454 (designated flhA454), which could allow expression of truncated FlhA proteins. All three flhA mutations severely inhibited transcription of the RpoN-dependent genes flaB and flgE in H. pylori B128. In contrast, levels of flaB and flgE transcripts in H. pylori ATCC 43504 bearing either flhA77 or flhA454, but not DflhA, were~60 % of wild-type levels. The FlhA 454 variant was detected in membrane fractions prepared from H. pylori ATCC 43504 but not H. pylori B128, which may account for the phenotypic differences in the flhA mutations of the two strains. Taken together, these findings suggest that only the N-terminal region of FlhA is needed for transcription of the RpoN regulon. Interestingly, expression of an flaB9-9xylE reporter gene in H. pylori ATCC 43504 bearing the flhA77 allele was about eightfold higher than that of a strain with the wild-type allele, suggesting that expression of flaB is not only regulated at the level of transcription but also regulated post-transcriptionally.

Flagellar biogenesis in Helicobacter pylori is regulated by a transcriptional hierarchy governed by three sigma factors, RpoD ( 80 ), RpoN ( 54 ), and FliA ( 28 ), that temporally coordinates gene expression with the assembly of the flagellum. Previous studies showed that loss of flagellar protein export apparatus components inhibits transcription of flagellar genes. The FlgS/FlgR two-component system activates transcription of RpoN-dependent genes though an unknown mechanism. To understand better the extent to which flagellar gene regulation is coupled to flagellar assembly, we disrupted flagellar biogenesis at various points and determined how these mutations affected transcription of RpoN-dependent (flaB and flgE) and FliA-dependent (flaA) genes. The MS ring (encoded by fliF) is one of the earliest flagellar structures assembled. Deletion of fliF resulted in the elimination of RpoN-dependent transcripts and an ϳ4-fold decrease in flaA transcript levels. FliH is a cytoplasmic protein that functions with the C ring protein FliN to shuttle substrates to the export apparatus. Deletions of fliH and genes encoding C ring components (fliM and fliY) decreased transcript levels of flaB and flgE but had little or no effect on transcript levels of flaA. Transcript levels of flaB and flgE were elevated in mutants where genes encoding rod proteins (fliE and flgBC) were deleted, while transcript levels of flaA was reduced ϳ2-fold in both mutants. We propose that FlgS responds to an assembly checkpoint associated with the export apparatus and that FliH and one or more C ring component assist FlgS in engaging this flagellar structure. T he bacterial flagellum is a complex nanomachine powered by an ion-driven rotary motor consisting of about 30 different types of proteins whose copy numbers range from a few to thousands (Fig. 1). The flagellum consists of three basic structures referred to as the basal body, hook, and filament (1). The basal body is an intricate complex that consists of the flagellar rod, rings, a motor, a switch complex, and a specialized type III secretion system (T3SS) that transports flagellar proteins across the cell membrane (1-3). The T3SS, also referred to as the flagellar protein export apparatus, consists of integral membrane proteins (FlhA, FlhB, FliO, FliP, FliQ, and FliR) which form an export pore located within the inner membrane, as well as cytoplasmic components (FliI, FliH, and FliJ) that deliver protein substrates to the export pore (4, 5). During flagellar assembly, the export apparatus initially transports rod-and hook-type substrates across the cell membrane into the lumen of the nascent flagellum (6, 7). Upon completion of the mature hook-basal body (HBB) structure, the export apparatus undergoes a conformational change that is accompanied by a switch in substrate specificity to filament-type substrates.Biogenesis of the bacterial flagellum involves a transcriptional hierarchy that is responsive to checkpoints in assembly so that expression of specific flagellar genes occurs as t...

Flagellar biogenesis in bacteria is a complex process in which the transcription of dozens of structural and regulatory genes is coordinated with the assembly of the flagellum. Although the overall process of flagellar biogenesis is conserved among bacteria, the mechanisms used to regulate flagellar gene expression vary greatly among different bacterial species. Many bacteria use the alternative sigma factor σ 54 (also known as RpoN) to transcribe specific sets of flagellar genes. These bacteria include members of the Epsilonproteobacteria (e.g., Helicobacter pylori and Campylobacter jejuni), Gammaproteobacteria (e.g., Vibrio and Pseudomonas species), and Alphaproteobacteria (e.g., Caulobacter crescentus). This review characterizes the flagellar transcriptional hierarchies in these bacteria and examines what is known about how flagellar gene regulation is linked with other processes including growth phase, quorum sensing, and host colonization.

Flagellar biogenesis in. FliO also appears to be required for wild-type levels of the export apparatus protein FlhA in the membrane. Interestingly, the periplasmic and cytoplasmic domains were somewhat dispensable for flagellar gene regulation and assembly, suggesting that these domains have relatively minor roles in flagellar synthesis.