Anammox Anaerobic ammonium oxidation

Figure 16.2 The redox intermediate, nitrite (N02 ), occupies a central position in the marine N-cycle. Shown are the various processes that are either sources or sinks for N02. Abbreviations include (clockwise from top) ANR = assimilatory nitrate reduction, Nit = nitrification, photolysis = UV-driven photocatalysis, DNR/DN = dissimilatory nitrate reduction/denitrification, ANR and Nit = as above, Anammox = Anaerobic ammonium oxidation.

An alternative bacterial route from NO to N2, where NH oxidation is coupled to NOj reduction in a process called anammox (anaerobic ammonium oxidation), dominates N2 production in many marine environments, but, unlike classical denitrification, it does not lead to the production of N2O. Together, denitrification and anammox close the nitrogen cycle by returning N2 gas back to the atmosphere. 

ANAMMOX [Anaerobic Ammonium Oxidation] A process for removing nitrogen from wastewaters. Most of the nitrogen is released as nitrogen gas. Developed and commercialized at the Delft University of Technology. The biochemical mechanism of the process was elucidated by M.S.M. Jetting for which he shared the Spinoza Prize in 2012. The first plant operated in 2001 and eleven plants were operating by 2012. See also Anammox. 

The anammox (anaerobic ammonium oxidation) bacteria carry out the following reaction in a strictly anaerobic medium ... 

Schmid MC et al. (2005) Biomarkers for in situ detection of anaerobic ammonium-oxidizing (Anammox) bacteria. Appl Environ Microbiol 71 1677-1684. 

The biogeochemical cycling of nitrogen is very much controlled by redox reactions. This perspective is presented in Figure 24.3 for the redox reactions that take place in the water column and sediments. The major pathways of reduction are nitrogen fixation, assimilatory nitrogen reduction, and denitrification. The major oxidation processes are nitrification and anaerobic ammonium oxidation (anammox). Each of these is described next in further detail. 

Ammonium oxidation (anammox) anaerobic NH4+ oxidation with NO3 this may be another mechanism whereby N is lost from natural systems. 

Figure 6.3 (Right) Schematic depiction of anammox cell showing the anammoxozome and nucleoid. (Left) Postulated pathway of anaerobic ammonium oxidation coupled to the ana-mmoxosome membrane resulting in a proton motive force and ATP synthesis via membrane-bound ATPases. HH, hydrazine hydrolase HZO, hydrazine oxidizing enzyme NIR, nitrite reductase. (Redrawn from van Niftrik etal., 2004 and Kuypers et al., 2006).

Engstrom, P., Dalsgaard, T., Hulth, S., and AUer, R. C. (2005). Anaerobic ammonium oxidation by nitrite (anammox) Implications for N-2 production in coastal marine sediments. Geochim. Cosmo-chim. Acta. 69(8), 2057—2065. 

Strous, M., van Gerven, E., Kuenen, J. G., andjetten, M. (1997). Effects of aerobic and microaerobic conditions on anaerobic ammonium-oxidizing (anammox) sludge. Appl. Environ. Microbiol. 63, 2446-2448. 

This process is termed Anammox for anaerobic ammonium oxidation and is catalyzed by a speciabzed group of planctomycetes bacteria first discovered in sewage reactors (Strous and Jetten, 2004). Again, the importance of Anammox in coral reef environments has not yet been considered. 

Anammox (i.e., anaerobic ammonium oxidation) is a recently discovered process that also results in N2 gas production and so is another form of denitrification (see Chapter 6 by Devol, this volume). The overall anammox reaction is NH4++N02 —> N2+2H2O. To date anammox rates have been quantified using parallel incubations with either N-labeled NH4+ or N-labeled and then analyzing the... 

Hietanen, S. (2007). Anaerobic ammonium oxidation (anammox) in sediments of the Gulf of Finland. Aquat. Microb. Ecol. 48, 197-205. 

Recent work has demonstrated that denitrification is not the only pathway producing N2. The anaerobic ammonium oxidation (anammox) pathway has received considerable attention and appears to account for the lack of ammonium in some denitrifying regimes (e.g., Dalsgaard et al., 2003 Kuypers et al., 2003). In addition to to trace denitrification, parallel incubations with NH4+ are... 

Jetten M. S. M., Wagner M., Fuerst L, van Loosdrecht M., Kuenen G., and Strous M. (2001) Microbiology and application of the anaerobic ammonium oxidation (anammox) process. Curr. Opinion Biotechnol. 12, 283-288. 

Figure 16 Summary of experiments from three sites on the continental shelf that quantified the absolute rates of anaerobic ammonium oxidation (i.e., anammox) and its contribution to total N2 production (i.e., anammox - -denitrification). The sites constitute a transect with Aarhus Bay closest to shore and Skagerrak S9 furthest from shore, (after Dalsgaard and Thamdmp, 2002).

Research since 1990 has greatly expanded our understanding of anaerobic metabolism. Novel microorganisms have been discovered, such as those performing anaerobic ammonium oxidation to N2 (anammox). These organisms were predicted to exist based on thermodynamic considerations, but have since been shown to contribute substantially to N2 production in some marine sediments. Organisms that were known to exist for sometime have been shown to perform... 

Another mechanism of fixed N loss that occurs in sediments and the water column is anaerobic ammonium oxidation, or anammox , in which nitrite (from nitrate reduction or ammonium oxidation) is used to oxidize ammonium to N2 (N02 + Nl-l4+ N2+ 2H2O). This process has unknown effects on isotope distributions in the ocean. The effects of anammox on N isotopes must depend on the organism-scale isotope effects, the sources of nitrite and ammonium substrates for the reaction, and the degree to which these substrates are consumed. For instance, if nitrate reduction by denitrifiers is the source of the nitrite, remineralization processes are the source of the ammonium, and both the nitrite and ammonium are completely consumed in the environment where anammox occurs, then the isotope discrimination would simplify to that of the nitrate reduction by denitrifiers averaged with any isotope discrimination during the remineralization that produces the needed ammonium. It should be noted that many water-column-derived... 

Major limiting factors controlling anaerobic ammonium oxidation reaction are the availability of nitrite and the competition for electron acceptors by heterotrophs. Soils and sediments with high organic matter content can create higher demand for electron acceptors (nitrite and nitrate). Under these conditions, anammox may not be able to keep up with denitrification when electron donor availability is very high. It is likely under available carbon-limiting conditions that some autotrophs... 

Dalsgaard, T., B. Thamdrup, and D. E. Canfield. 2005. Anaerobic ammonium oxidation (anammox) in the marine environment. Res. Microbiol. 156 457-464. 

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