Metabolism of Inorganic N Compounds by Ammonia-Oxidizing Bacteria

Abstract

Ammonia oxidizing bacteria extract energy for growth from the oxidation of ammonia to nitrite. Ammonia monooxygenase, which initiates ammonia oxidation, remains enigmatic given the lack of purified preparations. Genetic and biochemical studies support a model for the enzyme consisting of three subunits and metal centers of copper and iron. Knowledge of hydroxylamine oxidoreductase, which oxidizes hydroxylamine formed by ammonia monooxygenase to nitrite, is informed by a crystal structure and detailed spectroscopic and catalytic studies. Other inorganic nitrogen compounds, including NO, N2O, NO2, and N2 can be consumed and/or produced by ammonia-oxidizing bacteria. NO and N2O can be produced as byproducts of hydroxylamine oxidation or through nitrite reduction. NO2 can serve as an alternative oxidant in place of O2 in some ammonia-oxidizing strains. Our knowledge of the diversity of inorganic N metabolism by ammonia-oxidizing bacteria continues to grow. Nonetheless, many questions remain regarding the enzymes and genes involved in these processes and the role of these pathways in ammonia oxidizers.

Isotopic signatures of N2O produced by ammonia-oxidizing archaea from soils

“…The first N 2 O-yielding route in AOB is related to the activity of hydroxylamine oxidoreductase (HAO), which mediates the conversion of hydroxylamine to nitrite, the second step in ammonia oxidation. The second N 2 O-yielding route is through a denitrification pathway in AOB, the so-called nitrifier denitrification, where nitrite is reduced to NO and N 2 O (Wrage et al, 2001;Arp and Stein, 2003), as in the classical heterotrophic denitrification pathway.…”

Distributions and sea-to-air fluxes of nitrous oxide in the South China Sea and the West Philippines Sea

“…During autotrophic nitrification N 2 O can be formed by NH 4 þ -NH 2 OH (-NO)-NO 2 À either via the pathways NH 2 OH -N 2 O and NO -N 2 O (Arp and Stein, 2003;Stein and Yung, 2003) or via the pathway NO 2 À -NO -N 2 O (the latter is part of the so-called nitrifier-denitrification process) (Stein and Yung, 2003;Wrage et al, 2001). Nitrification is believed to be the main contributor to the production of N 2 O in seawater (Najjar, 1992;Bange and Andreae, 1999;Freing et al, 2012).…”

Strategies to Optimize Microbially-Mediated Mitigation of Greenhouse Gas Emissions from Landfill Cover Soils

“…(Hayatsu et al, 2008) 1.7.1. Nitrification Ammonia-and methane-oxidizing bacteria produce N 2 O during nitrification, specifically during the oxidation of hydroxylamine (NH 2 OH) to nitrite (NO 2 -) (Arp and Stein, 2003). The best characterized metabolic pathway for oxidation of ammonia to nitrite is performed by ammoniaoxidizing bacteria.…”

“…Ammonia-oxidizing bacteria have been shown to produce N 2 O when NO 2 -is used as an alternative electron acceptor under anoxic conditions, i.e., nitrifier denitrification, where NO 2 -is reduced to NO or N 2 O as in the classical heterotrophic denitrification pathway (Goreau et al, 1980;Poth and Focht, 1985;Arp and Stein, 2003). Studies using Nitrosomonas and Nitrosospira species have shown that ammonia-oxidizing bacteria are capable of reducing NO 2 -and produce N 2 O while doing so.…”