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

We measured N2O production by two species of primary chemoautotrophic nitri fying bacteria, Nitrosomonas europaea and Nitrosolobus multiformis, in medi a with different dissolved O-2 concentrations, Both species produced N2O ac ross a wide range of O-2 concentrations and after 48 h there was a large pe ak of NO production (3.2 nmol N2O cm(-3) cell suspension) by N. europaea at a dissolved concentration of 2.1 mg O-2 l(-1), whereas for N. multiformis the peak in N2O production was much smaller (1.6 nmol N2O cm(-3)), but it a lso occurred at a dissolved O-2 concentration of 2.1 mg O-2 l(-1). However at greater dissolved oxygen concentrations (between 24 and 37 mg O-2 l(-1)) , N. multiformis produced more N2O than N. europaea. The results are consis tent with both species producing N2O during NH4+ oxidation and with N. euro paea, producing a much larger amount of N2O during denitrification than N. multiformis. (C) 2001 Elsevier Science Ltd. All rights reserved.