Anammox Biochemistry: a Tale of Heme c Proteins.

Anaerobic ammonium-oxidizing (anammox) bacteria are one of the latest scientific discoveries in the biogeochemical nitrogen cycle. These microorganisms are able to oxidize ammonium (NH4 + ) with nitrite (NO2 - ) as the oxidant instead of oxygen and form dinitrogen (N2 ) as the end product. Recent research has shed a light on the biochemistry underlying anammox metabolism with two key intermediates, nitric oxide (NO) and hydrazine (N2 H4 ). Substrates and intermediates are converted exploiting the catalytic and electron-transfer potentials of c-type heme proteins known from numerous biochemical reactions and that have acquired new functionality in anammox biochemistry. On a global scale, anammox bacteria significantly contribute to the removal of fixed nitrogen from the environment and the process finds rapidly increasing interest in wastewater treatment.