A Tripartite Efflux System Affects Flagellum Stability in Helicobacter pylori

uses a cluster of polar, sheathed flagella for swimming motility. A search for homologs of proteins that were conserved in species that possess flagellar sheaths but were underrepresented in species with unsheathed flagella identified several candidate proteins. Four of the identified proteins are predicted to form part of a tripartite efflux system that includes two transmembrane domains of an ABC transporter (HP1487 and HP1486), a periplasmic membrane fusion protein (HP1488), and a TolC-like outer membrane efflux protein (HP1489). Deleting / and homologs in B128 resulted in reductions in motility and the number of flagella per cell. Cryo-electron tomography studies of intact motors of the Δ and Δ / mutants revealed many of the cells contained a potential flagellum disassembly product consisting of decorated L and P rings, which has been reported in other bacteria. Aberrant motors lacking specific components, including a cage-like structure that surrounds the motor, were also observed in the Δ mutant. These findings suggest a role for the HP1486-HP1489 tripartite efflux system in flagellum stability. Three independent variants of the Δ / mutant with enhanced motility were isolated. All three motile variants had the same frameshift mutation in , suggesting a role for FliL in flagellum disassembly.