Production of nitric oxide in Nitrosomonas europaea by reduction of nitrite

Nitrosomonas europaea and Nitrosovibrio sp. produced NO and N₂O during nitrification of ammonium. Less then 15% of the produced NO was due to chemical decomposition of nitrite. Production of NO and especially of N₂O increased when the bacteria were incubated under anaerobic conditions at decreasing flow rates of air, or at increasing cell densities. Low concentrations of chlorite (10 M) inhibited the production of NO and N₂, but not of nitrite indicating that NO and N₂O were not produced during the oxidative conversion of ammonium to nitrite. NO and N₂O were produced during reduction of nitrite with hydrazine as electron donor in almost stoichiometric quantities indicating that reduction of nitrite was the main source of NO and N₂O.