Production of NO and N2O by the heterotrophic nitrifier Alcaligenes faecalis parafaecalis under varying conditions of oxygen saturation

Production of NO and N2O by the heterotrophic nitrifier Alcaligenes faecalis subsp. parafaecalis was studied during growth in batch and continuous culture on peptone-meat extract medium. Depending on oxygen saturation level, medium redox status and amount of substrate supplied, the microorganisms produced 0.002-0.25 mg NO-N h(-1) (g protein)(-1) and 0.16-2.4 mg N2O-N h(-1) (g protein)(-1). Maximum rates of nitrogen oxides production were observed during peak events initiated by sudden changes of oxygen supply in the medium and were due to combined nitrification/denitrification taking place simultaneously within the cells. Based on model simulations of enzymatic kinetics of denitrification, possible mechanisms of increased nitrogen oxides production during periods of changes in oxygen supply are suggested.