Anaerobic ammonia oxidation with nitrogen dioxide by Nitrosomonas eutropha

Abstract

Nitrosomonas eutropha, an obligately lithoautotrophic bacterium, was able to nitrify and denitrify simultaneously under anoxic conditions when gaseous nitrogen dioxide (NO₂) was supplemented to the atmosphere. In the presence of gaseous NO₂, ammonia was oxidized, nitrite and nitric oxide (NO) were formed, and hydroxylamine occurred as an intermediate. Between 40 and 60% of the produced nitrite was denitrified to dinitrogen (N₂). Nitrous oxide (N₂O) was shown to be an intermediate of denitrification. Under an N₂ atmosphere supplemented with 25 ppm NO₂ and 300 ppm CO₂, the amount of cell protein increased by 0.87 mg protein per mmol ammonia oxidized, and the cell number of N. eutropha increased by 5.8 × 10⁹ cells per mmol ammonia oxidized. In addition, the ATP and NADH content increased by 4.3 μmol ATP (g protein)^–1 and 6.3 μmol NADH (g protein)^–1 and was about the same in both anaerobically and aerobically grown cells. Without NO₂, the ATP content decreased by 0.7 μmol (g protein)^–1, and the NADH content decreased by 1.2 μmol (g protein)^–1. NO was shown to inhibit anaerobic ammonia oxidation.