From Swimming to Sensing: The Multifunctional Flagella of Helicobacter

Helicobacter pylori is a motile bacterium that uses its high-torque flagella to colonize the diverse and challenging landscapes within the human stomach. H. pylori flagella possess numerous variations from canonical systems in motor dimensions, stator occupancy, flagellin composition, and the incorporation of additional basal body elements. Many, but not all, of these variations have been identified and characterized. H. pylori flagellar gene transcriptional regulation diverges from that of canonical models in its lack of a single master regulator, reliance on a hierarchy based on two σ factors, and use of a distributed set of regulatory checkpoints. Emerging evidence suggests H. pylori flagella play roles in mechanosensing and regulating the motile–sessile transition, relying on flagellar cage protein homologs of the type 4 pili PilO, PilN, and PilM and operating independently of c-di-GMP. The study of H. pylori flagella has revealed many surprises, and more surprises certainly await in this exciting field.