Channel-mediated potassium uptake in Helicobacter pylori is essential for gastric colonization

To date, the biological role of prokaryotic K+ channels remains unknown. Helicobacter pylori contains a gene encoding a putative K+ channel (HpKchA) of the two-transmembrane RCK (regulation of K+ conductance) domain family, but lacks known bacterial K+ uptake systems. A H. pylori Delta hpKchA mutant presented a strong growth defect at low K+ concentration, which was compensated by KCl addition. The role of the separate RCK domain was investigated in H. pylori by mutagenesis of its internal start codon, which led to a K+-dependent intermediate growth phenotype, consistent with RCK activating channel function. Tagging HpKchA C-terminally, we detected a 1:1 stoichiometry of the full-length HpKchA and the separate RCK domain. We constructed single amino-acid exchanges within the unusual selectivity filter of HpKchA (ATGFGA) in H. pylori and observed complete loss (G74A), a slight defect (G76A or F75G) or wild-type (A77D) channel function. HpKchA was essential for colonization of the murine stomach. These data show, for the first time, a biological function for a prokaryotic K+ channel, as a K+ uptake system, essential for the persistence of H. pylori in the gastric environment.