Reference Work Entry

The Prokaryotes

pp 457-495

Oxidation of Inorganic Nitrogen Compounds as an Energy Source

  • Eberhard Bock
  • , Michael Wagner


Life depends on the element nitrogen. In nature, nitrogen exists mainly in the oxidation states -III (NH3), O (N2), +I (N2O), +II (NO), +III (NO2), +IV (NO2), and +V (NO3). Owing to nitrogen transformations by the activity of living organisms and to chemical instability, any form of oxidation state has only a transient existence. Dinitrogen (N2) is the most inert and frequent constituent of the atmosphere.

Taking into account also abiotic transformations, three cycles of nitrogen can be distinguished:

  1. 1.

    The cycle of the atmosphere

  2. 2.

    The interaction between the atmosphere and the biosphere

  3. 3.

    The cycle of the biosphere


The nitrogen cycle mediated by the biosphere (Fig. 1) can also be characterized by mobilization and immobilization of nitrogen compounds. Most of the reactions are catalyzed exclusively by prokaryotes. By microbial nitrogen fixation, dinitrogen is reduced to ammonia and subsequently transferred to amino acids and assimilated into cell material. On the other hand, ...

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