Hydrogen and Nickel Metabolism inHelicobacterSpecies

Anaerobic microorganisms (such as clostridia) present in the large intestine of animals generate molecular hydrogen (H(2)) by fermentation using "H(2)-evolving" hydrogenases. The gas can also be detected in other tissues in mice, including the stomach, liver, spleen, or small intestine. It is established that this available H(2) can in turn be used as a source of energy by some pathogenic bacteria, including Helicobacter species like H. pylori and H. hepaticus. Both species possess one hydrogenase, which has been studied for H(2) oxidation characteristics and for its role in conferring animal colonization. On the basis of available annotated gene sequences, other Helicobacter species also appear to have one well-conserved respiratory, membrane-bound, nickel-iron-containing [NiFe] hydrogenase. Although H. pylori has been well-studied, many other (poorly studied) Helicobacter species likely represent a spectrum of emerging pathogens. The important role of hydrogenases in Helicobacter species is discussed, and the hydrogenases, their maturation/accessory factors, their regulation, as well as nickel transport and metabolism among the different species are compared.