C. Ryan Penton
The anammox reaction is anaerobic oxidation of ammonium coupled with nitrite reduction under anoxic conditions. This alternative nitrogen removal pathway was first proposed by Richards (1965), following observations of ammonium deficits in anoxic marine basins. Throughout most of the 20th century, ammonium was believed to be inert under anoxic conditions. Canonical denitrification liberates ammonium from organic matter during respiration, resulting in net accumulation in the sediment/soil profile. The proposed 'anammox' pathway allows for the removal of ammonium under purely anoxic conditions. Early evidence for the presence of this reaction was provided by marine sediment porewater profiles where the simultaneous disappearance of nitrite and ammonium was observed (Codispoti and Richards 1976; Cline and Richards 1972). Broda (1977) soon proposed a new type of bacteria responsible for these observations, a "chemosynthetic bacteria that oxidizes ammonia to nitrogen with O2 or nitrate as an oxidant", which was coined one of two "lithotrophs missing in nature". It was not until 1995 that the anammox process was confirmed in a fluidized bed reactor treating wastewater effluent (Mulder et al. 1995). The anammox reaction is a chemolithotrophic process in which 1 mol of ammonium is oxidized by 1 mol of nitrite to produce N2 gas in the absence of oxygen (Strous et al. 1999a, b):
Compared to denitrification, this process produces twice the amount of N2 per mol of nitrite consumed and increases N2 production in sediments where nitrification is limited. The bacteria responsible for this process were later identified as a deep-branching planctomycete with a peculiar morphology (Strous et al. 1999a, b).
C. Ryan Penton
540 Plant and Soil Sciences Bldg, Michigan State University, East Lansing, MI 48824, USA [email protected]
R. Margesin (ed.) Permafrost Soils, Soil Biology 16,
DOI: 10.1007/978-3-540-69371-0, © Springer-Verlag Berlin Heidelberg 2009
Despite the early suggestion that many microbes cannot be isolated in pure culture (Winogradsky 1949), the presence of a microbially mediated reaction that disputed the notion that ammonium was inert under anoxic conditions was initially regarded with skepticism. Since then, numerous studies have identified anammox as a key process in the global nitrogen cycle.
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