Effects of ammonia (A), nitrite (B), temperature (C), pH (D), and salinity (E) on the ammonia oxidation activities of strain MY1 and N. europaea. The same AFM and cultivation conditions were used for strain MY1 and N. europaea. Ammonia oxidation activity was indicated by the amount of nitrite accumulated. In the study on nitrite inhibition, ammonia consumption was determined. The error bars represent standard deviations from triplicate experiments.