A Positively Selected -R88H Mutation Enhances Helicobacter pylori Fitness in a High-Salt Environment and Alters Fur-Dependent Regulation of Gene Expression.

Both Helicobacter pylori infection and a high-salt diet are risk factors for gastric cancer. We previously showed that a mutation in (encoding the ferric uptake regulator variant Fur-R88H) was positively selected in H. pylori strains isolated from experimentally infected Mongolian gerbils receiving a high-salt diet. In the present study, we report that continuous H. pylori growth in high-salt conditions also leads to positive selection of the -R88H mutation. Competition experiments with strains containing wild-type or -R88H, each labeled with unique nucleotide barcodes, showed that the -R88H mutation enhances H. pylori fitness under high-salt conditions but reduces H. pylori fitness under routine culture conditions. The fitness advantage of the -R88H mutant under high-salt conditions was abrogated by the addition of supplemental iron. To test the hypothesis that the -R88H mutation alters the regulatory properties of Fur, we compared the transcriptional profiles of strains containing wild-type or -R88H. Increased transcript levels of , which encodes a predicted TonB-dependent outer membrane transporter, were detected in the -R88H variant compared to those in the strain containing wild-type under both high-salt and routine conditions. Competition experiments showed that contributes to H. pylori fitness under both high-salt and routine conditions. These results provide new insights into mechanisms by which the -R88H mutation confers a selective advantage to H. pylori in high-salt environments.