A Tripartite Efflux System Affects Flagellum Stability in Helicobacter pylori

Abstract

Helicobacter pylori uses a cluster of polar, sheathed flagella for swimming motility. A search for homologs of H. pylori proteins that were conserved in Helicobacter species that possess flagellar sheaths but were underrepresented in Helicobacter 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 hp1486/hp1487 and hp1489 homologs in H. pylori B128 resulted in reductions in motility and the number of flagella per cell. Cryo-electron tomography studies of intact motors of the Δhp1489 and Δhp1486/hp1487 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 Dhp1489 mutant. These findings suggest a role for the H. pylori HP1486-HP1489 tripartite efflux system in flagellum stability. Three independent variants of the Δhp1486/hp1487 mutant with enhanced motility were isolated. All three motile variants had the same frameshift mutation in fliL, suggesting a role for FliL in flagellum disassembly.

Motility of Different Gastric Helicobacter spp.

“…When comparing the proteins encoded in the genomes of Helicobacters that have flagellar sheaths (FS+) against Helicobacters that have unsheathed flagella (FS-), the homologs of nearly 40 proteins were found significantly more frequently in the FS+ Helicobacter species compared to FS- Helicobacter species. Four of these proteins, HP1486, HP1487, HP1488, and HP1489, were found exclusively in the FS+ Helicobacter species and appear to be part of a tripartite efflux system [ 25 ]. A comparative genomics analysis to identify potential metabolic and virulence gene potentials in gastric versus enterohepatic Helicobacter species has been discussed [ 26 ].…”