Helicobacter Flagella, Motility and Chemotaxis
Melanie Rust, Tobias Schweinitzer, and Christine Josenhans
from: Helicobacter pylori: Molecular Genetics and Cellular Biology (Edited by: Yoshio Yamaoka). Caister Academic Press, U.K. (2008)
Abstract
All gastric and enterohepatic Helicobacter species are highly motile. Comparative genomic analysis in different Helicobacter species and related bacteria in recent years have facilitated the analysis of genus-, species- and niche-specific properties. The characteristic sheathed flagellar filaments of helicobacters are composed of two copolymerized flagellins, FlaA and FlaB. Experiments in different animal models with Helicobacter pylori, Helicobacter mustelae and Helicobacter felis showed that flagellar motility is essential for Helicobacter species to colonize the gastric mucus. H. pylori has homologs of almost all flagellar structural proteins known from Enterobacteriaceae, but the regulatory network of H. pylori motility genes, which has been investigated in some detail, lacks a flhCD master operon and other regulatory factors, and relies on a three-tiered hierarchical regulatory system with RpoN as the central sigma factor. H. pylori shows taxis (directed motility) towards urea, amino acids, and bicarbonate, and moves away from low pH. Recently, it has been shown in several in vivo systems that chemotaxis in addition to motility is required for colonisation, and that H. pylori and H. felis reside in a very narrow layer of the gastric mucus, close to the gastric epithelium, where they are guided by the mucus pH gradient. So far, the mucus pH gradient seems to be the most important sensing stimulus in vivo for H. pylori orientation. However, it is still not completely clear which combinations of horizontal and vertical chemical gradients are used by H. pylori in vivo to maintain an optimal position in the gastric mucus layer. The chemotaxis systems of H. pylori and H. hepaticus are genetically similar to the Salmonella system as based on genomic analysis, but extensive functional analyses on the proteins involved have just been started. A dominant property of the H. pylori sensing system from recent in vivo and in vitro studies seems to be pH taxis read more ...
