Oxygen and nitrogen production by an ammonia-oxidizing archaeon

Abstract

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

Mapping Microbial Abundance and Prevalence to Changing Oxygen Concentration in Deep-Sea Sediments Using Machine Learning and Differential Abundance

“…This finding could be due to the presence of oxygen below the detection limit of our measurement apparatus and rapid consumption of oxygen, but nevertheless underpins Nitrosopumilales' impact as nitrifiers along AMOR, and also shows that oxygen may not be the best variable to track presence and abundance for this order in deep-sea sediments. Alternatively, it could suggest that this group is able to oxidise ammonia under anoxic conditions, as recently shown for a member of this family, which is capable of producing its own oxygen (Kraft et al, 2022 ). The lack of differential abundance for many Nitrosopumilales representatives between oxygen-rich and anoxic sediments, and their presence in deep anoxic sediments (Kirkpatrick et al, 2019 ) as well as the aforementioned recent evidence of oxygen production in one representative (Kraft et al, 2022 ), furthermore underpins the complex relationship between this order and geochemical transition zones where the sources of required terminal electron acceptors may be hard to track.…”

How low can they go? Aerobic respiration by microorganisms under apparent anoxia

“…Recent results, indicate that an ammonia-oxidizing archaeon might also produce its own molecular O 2 from nitrite (Kraft et al . 2022 ). These intriguing metabolic strategies highlight that the classification of aerobe/anaerobe is nonbinary and yet has profoundly shaped the vocabulary we use to describe microbial adaptations to the environments around us.…”

Phylogenomic evidence for the Origin of Obligately Anaerobic Anammox Bacteria around the Great Oxidation Event

“…Importantly, O 2 is necessary, although a trace amount is feasible, to extant nitrifying organisms for the oxidation of ammonium to nitrite and nitrate [50][51][52] . We noticed that a recent study 53 reports the ability of the model ammonia-oxidizing archaeal species (Nitrosopumilus maritimus) to continue ammonia oxidation after consuming all supplied O 2 by nitric oxide disproportionation to generate O 2 , but the underlying genetic pathway is not known, making it difficult to extrapolate this mechanism to any other ammonia-oxidizing organisms. Hence the rise of oxygen almost certainly triggered the growth of the nitrite/nitrate reservoir, and therefore potentially provided one of the key substrates for anammox bacteria.…”