Different sensitivities to oxygen of nitrous oxide production by Nitrosomonas europaea and Nitrosolobus multiformis

We measured N2O production by two species of primary chemoautotrophic nitrifying bacteria, Nitrosomonas europaea and Nitrosolobus multiformis, in media with different dissolved O2 concentrations. Both species produced N2O across a wide range of O2 concentrations and after 48 h there was a large peak of N2O production (3.2 nmol N2O cm−3 cell suspension) by N. europaea at a dissolved concentration of 2.1 mg O2 l−1, whereas for N. multiformis the peak in N2O production was much smaller (1.6 nmol N2O cm−3), but it also occurred at a dissolved O2 concentration of 2.1 mg O2 l−1. However at greater dissolved oxygen concentrations (between 24 and 37 mg O2 l−1), N. multiformis produced more N2O than N. europaea. The results are consistent with both species producing N2O during NH4+ oxidation and with N. europaea, producing a much larger amount of N2O during denitrification than N. multiformis.