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 x 10(9) 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.

Ammonium and hydroxylamine uptake and accumulation in Nitrosomonas

“…Precultures of Nsm. europaea (ATCC 19178), Nitrosomonas eutropha strain N904 and Nitrosolobus multiformis (ATCC 25196) were grown aerobically in 1 l Erlenmeyer flasks containing 400 ml mineral medium (Schmidt & Bock, 1997). The cultures were grown for 1-2 weeks in the dark at 28 uC.…”

“…The cultures were grown for 1-2 weeks in the dark at 28 uC. Schmidt & Bock (1997) (ammonium), according to van de Graaf et al (1996) (nitrite, nitrate) and by a modified method according to Verstraete & Alexander (1972) (NH 2 OH). The protein concentration was determined according to Bradford (1976).…”

“…Later, Abeliovich & Vonshak (1992) and Bock et al (1995) described a heterotrophic and hydrogen-dependent denitrification as an alternative pathway. Evidence for another anoxic mechanism to gain energy was given by Schmidt & Bock (1997) by characterizing the nitrogen dioxidedependent ammonia oxidation known as the NOx-cycle. This metabolism is obviously the connecting link between anoxic denitrification and oxic nitrification.…”

“…This metabolism is obviously the connecting link between anoxic denitrification and oxic nitrification. The nitrogen oxides, NO and NO 2 , have been shown to be obligatory intermediates in the oxidation of ammonia, and they have regulatory effects on the metabolism of the nitrifiers (Schmidt & Bock, 1998;Schmidt et al, 2001aSchmidt et al, -c, 2002Zart et al, 2000).…”

Anaerobic ammonium oxidation for treatment of ammonium-rich wastewaters

“…Nitrosomonas eutropha, a classic aerobic ammonium oxidizer, belongs to one group which oxidizes ammonium with NO 2 as electron acceptor under anoxic conditions (Schmidt and Bock, 1997). The so-called ANAMMOX bacteria actually are specialized into the other group of deep-branching planctomycetes (Table 1).…”