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Timestamp: 2019-04-20 02:57:36+00:00

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This chapter concentrates on the mechanisms used by Helicobacter pylori to maintain its ion homeostasis, emphasizing metal cations. Maintaining ion homeostasis requires both sensor systems to detect the cytoplasmic ion concentration and effector systems to restore normal cell conditions, or to cope with stress caused by ion imbalance. Iron availability is usually low in most environments, and thus bacteria require specific high-affinity iron acquisition systems. The adaptation of H. pylori to life in the gastric mucosa seems to have led to a more pronounced role of nickel in its metabolism, for example, in its role as an essential cofactor of urease, which mediates acid resistance of H. pylori. Urease plays a central role in the pathogenesis of H. pylori infection and catalyzes the conversion of urea into carbon dioxide and ammonia. The latter is able to neutralize gastric acid and offer protection to H. pylori against the low pH in the stomach. Concerning competition for nutrients as well as the acidic pH, the niche differs considerably from the environments most other bacteria colonize. Elements of its systems for ion metabolism and transport seem to reflect specific adaptations of H. pylori to its ecological niche, and the functions and mechanisms involved might be different from the paradigms developed for enteric bacteria like Escherichia coli. H. pylori contains relatively low numbers of ion transport systems, except for nickel and iron. These two ions can be transported by two or more systems, indicating their importance in the physiology of H. pylori.
Schematic representation of the mechanisms involved in maintaining ion homeostasis.
Schematic overview of ion transport systems of H. pylori. The ion transported and the direction of transport are indicated. OM, outer membrane; CM, cytoplasmic membrane. Ion transporters are grouped depending on the direction of transport: importers at the top, and exporters at the bottom.
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