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Mechanisms and Control of NO2− Inhibition of Anaerobic Ammonium Oxidation (Anammox)

ABSTRACT: Nitrite (NO2−), one of the main substrates in the anaerobic ammonium oxidation (anammox) process, has the potential to inhibit anammox bacteria. The sensitivity of anammox cells with different energy status to NO2− was evaluated, and addition of nitrate (NO3−) inhibition on the basis of narK gene with the putative function of facilitating NO3−/NO2− antiporter. The results showed that the resistance of anammox bacteria to NO2− inhibition follows the order: active‐cells > starved‐cells > resting‐cells > starved‐/resting‐cells. Anammmox resting cells have increasing tolerance to NO2− in the pH range from 7.0 to 7.5. Dissipating the proton gradient by using carbonyl cyanide m‐chlorophenyl hydrazine (CCCP) caused severe inhibition at all pH values including pH = 7.5. Addition of NO3− enabled activity recovery of NO2−‐inhibited anammox bacteria regardless of whether the proton gradient was disrupted or not, supporting the hypothesis of NO3−‐dependent detoxification via a secondary transport system.