Anaerobic hydrogen oxidation

Acetogens such as Clostridium and Acetobacterium can ferment sugars to acetate but can also use carbon dioxide and hydrogen to produce acetate and water:

This membrane-associated hydrogenase couples the reaction to the pumping of protons or sodium. The re-entry into the cell of these cations via ATPase leads to ATP generation. Most organisms carrying out this reaction are Gram-positive Bacteria, but the Archaeal methanogens can also oxidize hydrogen anaerobically to yield methane and water.