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Helicobacter pullorum  is an avian bacterium that causes gastroenteritis, intestinal bowel and hepatobiliary diseases in humans. Although  H. pullorum  has been shown to activate the mammalian innate immunity with release of nitric oxide (NO), the proteins that afford protection against NO and reactive nitrogen species (RNS) remain unknown. Here several protein candidates of  H. pullorum , namely a truncated (TrHb) and a single domain haemoglobin (SdHb), and three peroxiredoxin-like proteins (Prx1, Prx2 and Prx3) were investigated. We report that the two haemoglobin genes are induced by RNS, and that SdHb confers resistance to nitrosative stress both  in vitro  and in macrophages. For peroxiredoxins, the  prx2  and  prx3  expression is enhanced by peroxynitrite and hydrogen peroxide, respectively. Mutation of  prx1  does not alter the resistance to these stresses, while the single ∆ prx2  and double ∆ prx1 ∆ prx2  mutants have decreased viability. To corroborate the physiological data, the biochemical analysis of the five recombinant enzymes was done, namely by stopped-flow spectrophotometry. It is shown that  H. pullorum  SdHb reacts with NO much more quickly than TrHb, and that the three Prxs react promptly with peroxynitrite, Prx3 displaying the highest reactivity. Altogether, the results unveil SdHb and Prx3 as major protective systems of  H. pullorum  against nitrosative stress.

Nitrosative stress defences of the enterohepatic pathogenic bacterium Helicobacter pullorum