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 (NH 4 + ) with nitrite (NO 2 − ) as the oxidant instead of oxygen and form dinitrogen (N 2 ) 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 (N 2 H 4 ). 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.