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

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.