Microbial hydrogenases and the global hydrogen cycle

Hydrogen is an atmospheric trace gas which is mainly decomposed in soils. Already in the 1970s it was obvious that the decomposition process must be based on biological activity. However, it took more than 40 years until the decomposition process was finally understood. Today we know that nickel-iron hydrogenases of the group 5 are responsible for the oxidation of the atmospheric hydrogen. These hydrogenases are mainly found in Actinobacteria, e.g., Streptomyces or Mycobacterium, which are common microorganisms in soils.