Functional analysis of the Helicobacter pylori flagellar switch proteins

Helicobacter pylori uses flagellum-mediated chemotaxis to promote infection. Bacterial flagella change rotational direction by changing the state of the flagellar motor via a subcomplex referred to as the switch. Intriguingly, the H. pylori genome encodes four switch complex proteins, FliM, FliN, FliY, and FliG, instead of the more typical three of Escherichia coli or Bacillus subtilis. Our goal was to examine whether and how all four switch proteins participate in flagellation. Previous work determined that FliG was required for flagellation, and we extend those findings to show that all four switch proteins are necessary for normal numbers of flagellated cells. Furthermore, while fliY and fliN are partially redundant with each other, both are needed for wild-type levels of flagellation. We also report the isolation of an H. pylori strain containing an R54C substitution in fliM, resulting in bacteria that swim constantly and do not change direction. Along with data demonstrating that CheY-phosphate interacts with FliM, these findings suggest that FliM functions in H. pylori much as it does in other organisms.