Nitric oxide-dependent anaerobic ammonium oxidation

Nitric oxide (NO) has several important functions in biology and atmospheric chemistry as a toxin, signaling molecule, ozone depleting agent and the precursor of the greenhouse gas nitrous oxide (N2O). Even though NO is a potent oxidant, and was available on earth earlier than oxygen, its direct use by microorganisms for growth was not demonstrated before. Using physiological experiments, metatranscriptomics and metaproteomics, here we show that anaerobic ammonium-oxidizing (anammox) bacterium Kuenenia stuttgartiensis grow by coupling ammonium oxidation to NO reduction, and produce only N2. Such a metabolism could have existed on early earth, and has implications in controlling N2O and NO emissions both from natural and manmade ecosystems, where anammox bacteria contribute significantly to N2 release to the atmosphere.