Anammox and denitrification are suppressed by nanomolar concentrations of oxygen

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Why is it important?

The removal of fixed nitrogen via anammox and denitrification associated with low O2 concentrations in oceanic oxygen minimum zones (OMZ) is a major sink in oceanic N budgets, yet the sensitivity and dynamics of these processes with respect to O2 are poorly known. The present study elucidated how nanomolar O2 concentrations affected nitrogen removal rates and expression of key nitrogen cycle genes in water from the eastern South Pacific OMZ, applying state-of-the-art 15 N techniques and metatranscriptomics. Rates of both denitrification and anammox responded rapidly and reversibly to changes in O2 , but denitrification was more O2 sensitive than anammox. The transcription of key nitrogen cycle genes did not respond as clearly to O2 , although expression of some of these genes decreased. Quantifying O2 sensitivity of these processes is essential for predicting through which pathways and in which environments, from wastewater treatment to the open oceans, nitrogen removal may oc-cur.