Oxygen and nitrogen production by an ammonia-oxidizing archaeon

Consuming oxygen, but making it too For marine microbes, there are myriad biological reactions involved in the cycling of nutrients and the generation of energy. Availability of oxygen is crucial for many species’ metabolism. Kraft et al . were surprised to find that pure cultures of an ammonia-oxidizing archaean (AOA) (see the Perspective by Martens-Habbena and Qin), Nitosopumilus maritimus , were able to regenerate small amounts of oxygen when placed under anoxic conditions. Isotope labeling of nitrogen species revealed a series of reactions transforming nitrite, the expected metabolic end product, into nitric oxide, nitrous oxide, and, eventually, dinitrogen. Oxygen was also formed, likely from nitric oxide disproportionation, but was mostly consumed, which is consistent with the overall aerobic metabolism of AOA. These organisms can be found in oxygen-depleted waters and may benefit from producing oxygen from nitrite under these conditions. —MAF