The diverse antioxidant systems of Helicobacter pylori

Summary The gastric pathogen Helicobacter pylori induces a strong inflammatory host response, yet the bacterium maintains long‐term persistence in the host. H. pylori combats oxidative stress via a battery of diverse activities, some of which are unique or newly described. In addition to using the well‐studied bacterial oxidative stress resistance enzymes superoxide dismutase and catalase, H. pylori depends on a family of peroxiredoxins (alkylhydroperoxide reductase, bacterioferritin co‐migratory protein and a thiol‐peroxidase) that function to detoxify organic peroxides. Newly described antioxidant proteins include a soluble NADPH quinone reductase (MdaB) and an iron sequestering protein (NapA) that has dual roles – host inflammation stimulation and minimizing reactive oxygen species production within H. pylori . An H. pylori arginase attenuates host inflammation, a thioredoxin required as a reductant for many oxidative stress enzymes is also a chaperon, and some novel properties of KatA and AhpC were discovered. To repair oxidative DNA damage, H. pylori uses an endonuclease (Nth), DNA recombination pathways and a newly described type of bacterial MutS2 that specifically recognizes 8‐oxoguanine. A methionine sulphoxide reductase (Msr) plays a role in reducing the overall oxidized protein content of the cell, although it specifically targets oxidized Met residues. H. pylori possess few stress regulator proteins, but the key roles of a ferric uptake regulator (Fur) and a post‐transcriptional regulator CsrA in antioxidant protein expression are described. The roles of all of these antioxidant systems have been addressed by a targeted mutant analysis approach and almost all are shown to be important in host colonization. The described antioxidant systems in H. pylori are expected to be relevant to many bacterial‐associated diseases, as genes for most of the enzymes carrying out the newly described roles are present in a number of pathogenic bacteria.