A hydrogen-sensing multiprotein complex controls aerobic hydrogen metabolism in Ralstonia eutropha

H₂ is an attractive energy source for many microorganisms and is mostly consumed before it enters oxic habitats. Thus aerobic H₂-oxidizing organisms receive H₂ only occasionally and in limited amounts. Metabolic adaptation requires a robust oxygen-tolerant hydrogenase enzyme system and special regulatory devices that enable the organism to respond rapidly to a changing supply of H₂. The proteobacterium Ralstonia eutropha strain H16 that harbours three [NiFe] hydrogenases perfectly meets these demands. The unusual biochemical and structural properties of the hydrogenases are described, including the strategies that confer O₂ tolerance to the NAD-reducing soluble hydrogenase and the H₂-sensing regulatory hydrogenase. The regulatory hydrogenase that forms a complex with a histidine protein kinase recognizes H₂ in the environment and transmits the signal to a response regulator, which in turn controls transcription of the hydrogenase genes.