ABSTRACT
Molecular hydrogen is biologically produced in large amounts during the anaerobic decomposition of organic material. Depending on the hydrogen acceptor available in the habitat, hydrogen is oxidized by a variety of microorganisms, with the production of methane, hydrogen sulfide, or nitrogen under anaerobic conditions or water if hydrogen diffuses into aerobic zones. The organisms differ profoundly in taxonomic position, cell structure and properties of their hydrogen activating system and its regulation. The ability to use the energy derived from an inorganic energy source for the assimilation of an inorganic carbon source places hydrogen bacteria among the chemolithoautotrophic organisms. Hydrogen bacteria can, however, adapt equally well to a chemoorganotrophic way of life, using a wide variety of organic substrates. Oxygen strongly inhibits the synthesis of the membrane-bound hydrogenase from Aquaspirillum autotrophicum, with complete inhibition in the presence of 0.3 atm oxygen.
