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Nitrogen cycle

NitrificationFrom Wikipedia, the free encyclopedia

Nitrificationis the biological oxidation of ammonia

or ammonium to nitrite followed by the oxidation of

the nitrite to nitrate.[1]The transformation of

ammonia to nitrite is usuallythe rate limiting step ofnitrification. Nitrification is an important step in the

nitrogen cycle in soil. Nitrification is an aerobic

process performedby small groups of autotrophic

bacteria and archaea. This process was discovered

by the Russian microbiologist, Sergei Winogradsky.

Contents

1 Microbiology and ecology

2 Chemistry

3 Nitrification in the marine environment

4 Soil Conditions controlling nitrification

rates

5 See also

6 References

7 External links

Microbiology and ecology

The oxidation of ammonia into nitrite is performed by two groups of organisms, ammonia-oxidizing

bacteria (AOB) and ammonia-oxidizing archaea (AOA[2]).[3]AOB can be found amongthe -

proteobacteria and gammaproteobacteria.[4]Currently, two AOA,Nitrosopumilus maritimusand

Nitrososphaera viennensis, have been isolated anddescribed.[5]

In soils the most studiedAOB belong tothe generaNitrosomonasandNitrosococcus. Although in soils ammonia oxidation occurs by both AOB

and AOA, AOA dominate inboth soilsand marine environments,[2][6][7]suggesting that

Thaumarchaeotamay be greater contributors to ammonia oxidation in these environments.[2]

The second step (oxidation of nitrite into nitrate) is done (mainly) by bacteria of the genusNitrobacter

andNitrospira. Both steps are producing energy to be coupled to ATP synthesis. Nitrifying organisms

are chemoautotrophs, and use carbon dioxide as their carbon source for growth. Some AOB possess the

enzyme, urease, which catalyzes the conversion of the urea molecule to two ammonia molecules and one

carbon dioxide molecule.Nitrosomonas europaea, as well as populations of soil-dwelling AOB, have

been shown to assimilate the carbon dioxide released by the reaction to make biomass via the CalvinCycle, and harvest energy by oxidizing ammonia (the other product of urease) to nitrite. This feature

may explain enhanced growth of AOB in the presence of urea in acidic environments.[8]
http://en.wikipedia.org/wiki/Calvin_Cyclehttp://en.wikipedia.org/wiki/Calvin_Cyclehttp://en.wikipedia.org/wiki/Chemotrophhttp://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/Carbonhttp://en.wikipedia.org/wiki/Thaumarchaeotahttp://en.wikipedia.org/wiki/Nitrosomonashttp://en.wikipedia.org/w/index.php?title=Nitrosococcus&action=edit&redlink=1http://en.wikipedia.org/wiki/File:Nitrogen_Cycle.svghttp://en.wikipedia.org/wiki/File:Nitrogen_Cycle.svghttp://en.wikipedia.org/wiki/File:Nitrogen_Cycle.svghttp://en.wikipedia.org/wiki/File:Nitrogen_Cycle.svghttp://en.wikipedia.org/wiki/File:Nitrogen_Cycle.svghttp://en.wikipedia.org/wiki/File:Nitrogen_Cycle.svghttp://en.wikipedia.org/wiki/File:Nitrogen_Cycle.svghttp://en.wikipedia.org/wiki/File:Nitrogen_Cycle.svghttp://en.wikipedia.org/wiki/File:Nitrogen_Cycle.svghttp://en.wikipedia.org/wiki/File:Nitrogen_Cycle.svghttp://en.wikipedia.org/wiki/File:Nitrogen_Cycle.svghttp://en.wikipedia.org/wiki/Ammoniumhttp://en.wikipedia.org/wiki/Ammoniumhttp://en.wikipedia.org/wiki/Nitritehttp://en.wikipedia.org/wiki/File:Nitrogen_Cycle.svghttp://en.wikipedia.org/wiki/Redoxhttp://en.wikipedia.org/wiki/Ammoniahttp://en.wikipedia.org/wiki/File:Nitrogen_Cycle.svghttp://en.wikipedia.org/wiki/Calvin_Cyclehttp://en.wikipedia.org/wiki/Biomass_(ecology)http://en.wikipedia.org/wiki/Carbonhttp://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/Chemotrophhttp://en.wikipedia.org/wiki/Nitrospirahttp://en.wikipedia.org/wiki/Nitrobacterhttp://en.wikipedia.org/wiki/Thaumarchaeotahttp://en.wikipedia.org/w/index.php?title=Nitrosococcus&action=edit&redlink=1http://en.wikipedia.org/wiki/Nitrosomonashttp://en.wikipedia.org/wiki/Gammaproteobacteriahttp://en.wikipedia.org/wiki/%CE%92-proteobacteriahttp://en.wikipedia.org/wiki/Archaeahttp://en.wikipedia.org/wiki/Bacteriahttp://en.wikipedia.org/wiki/Sergei_Winogradskyhttp://en.wikipedia.org/wiki/Microbiologisthttp://en.wikipedia.org/wiki/Russiahttp://en.wikipedia.org/wiki/Aerobichttp://en.wikipedia.org/wiki/Soilhttp://en.wikipedia.org/wiki/Nitrogen_cyclehttp://en.wikipedia.org/wiki/Nitratehttp://en.wikipedia.org/wiki/Nitritehttp://en.wikipedia.org/wiki/Nitritehttp://en.wikipedia.org/wiki/Ammoniumhttp://en.wikipedia.org/wiki/Ammoniahttp://en.wikipedia.org/wiki/Redoxhttp://en.wikipedia.org/wiki/Nitrogen_cyclehttp://en.wikipedia.org/wiki/File:Nitrogen_Cycle.svg


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In most environments, organisms are present that will complete both steps of the process, yielding

nitrate as the final product. However, it is possible to design systems in which nitrite is formed (the

Sharon process).

Nitrification is important in agricultural systems, where fertilizer is often applied as ammonia.

Conversion of this ammonia to nitrate increases nitrogen leaching because nitrate is more water-soluble

than ammonia.

Nitrification also plays an important role in the removal of nitrogen from municipal wastewater. The

conventional removal is nitrification, followed by denitrification. The cost of this process resides mainly

in aeration (bringing oxygen in the reactor) and the addition of an external carbon source (e.g.,

methanol) for the denitrification.

Nitrification can also occur in drinking water. In distribution systems where chloramines are used as the

secondary disinfectant, the presence of free ammonia can act as a substrate for ammonia-oxidizing

microorganisms. The associated reactions can lead to the depletion of the disinfectant residual in the

system.[9]The addition of chlorite ion to chloramine-treated water has been shown to control

nitrification.[10][11]

Together with ammonification, nitrification forms a mineralization process that refers to the complete

decomposition of organic material, with the release of available nitrogen compounds. This replenishes

the nitrogen cycle.

Chemistry

Nitrification is a process of nitrogen compound oxidation (effectively, loss of electrons from the

nitrogen atom to the oxygen atoms):

1. 2 NH4++ 3 O2 2 NO2

-+ 2 H2O + 4 H+(Nitrosomonas)

2. 2 NO2-+ O2 2 NO3

-(Nitrobacter, Nitrospina)

3. NH3+ O2 NO2+ 3H++ 2e

4. NO2+ H2O NO3

+ 2H++ 2e

Nitrification in the marine environment

In the marine environment, nitrogen is often the limiting nutrient, so the nitrogen cycle in the ocean is of

particular interest.[12][13]The nitrification step of the cycle is of particular interest in the ocean because it

creates nitrate, the primary form of nitrogen responsible for "new" production. Furthermore, as the ocean

becomes enriched in anthropogenic CO2, the resulting decrease in pH could lead to decreasing rates of

nitrification. Nitrification could potentially become a "bottleneck" in the nitrogen cycle.[14]

Nitrification, as stated above, is formally a two-step process; in the first step ammonia is oxidized to

nitrite, and in the second step nitrite is oxidized to nitrate. Different microbes are responsible for each

step in the marine environment. Several groups of ammonia-oxidizing bacteria (AOB) are known in themarine environment, includingNitrosomonas,Nitrospira, andNitrosococcus. All contain the functional

gene ammonia monooxygenase (AMO) which, as its name implies, is responsible for the oxidation of

ammonia.[2][13]More recent metagenomic studies have revealed that some Thaumarchaeota (formerly
http://en.wikipedia.org/wiki/Thaumarchaeotahttp://en.wikipedia.org/wiki/Metagenomichttp://en.wikipedia.org/wiki/Ammonia_monooxygenasehttp://en.wikipedia.org/w/index.php?title=Nitrosococcus&action=edit&redlink=1http://en.wikipedia.org/wiki/Nitrospirahttp://en.wikipedia.org/wiki/Nitrosomonashttp://en.wikipedia.org/wiki/Ammonia-oxidizing_bacteriahttp://en.wikipedia.org/wiki/Nitritehttp://en.wikipedia.org/wiki/Oxidizedhttp://en.wikipedia.org/wiki/Ammoniahttp://en.wikipedia.org/wiki/PHhttp://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/Anthropogenichttp://en.wikipedia.org/wiki/F-ratiohttp://en.wikipedia.org/wiki/Nitratehttp://en.wikipedia.org/wiki/Nitrogen_cyclehttp://en.wikipedia.org/wiki/Limiting_nutrienthttp://en.wikipedia.org/wiki/Marine_environmenthttp://en.wikipedia.org/wiki/Redoxhttp://en.wikipedia.org/wiki/Nitrogen_cyclehttp://en.wikipedia.org/wiki/Mineralization_(soil)http://en.wikipedia.org/wiki/Ammonificationhttp://en.wikipedia.org/wiki/Chloramineshttp://en.wikipedia.org/wiki/Methanolhttp://en.wikipedia.org/wiki/Aerationhttp://en.wikipedia.org/wiki/Denitrificationhttp://en.wikipedia.org/wiki/Wastewaterhttp://en.wikipedia.org/wiki/Nitrogenhttp://en.wikipedia.org/w/index.php?title=Sharon_process&action=edit&redlink=1


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Crenarchaeota) possess AMO. Thaumarchaeotes are abundant in the ocean and some species have a 200

times greater affinity for ammonia than AOB, leading researchers to challenge the previous belief that

AOB areprimarily responsible for nitrification in the ocean.[15]Furthermore, though nitrification is

classicallythought to be vertically separated from primary production because the oxidation of nitrogen

by bacteria is inhibited by light, nitrification by AOA does not appear to be light inhibited, meaning that

nitrificationis occurring throughout the water column, challenging the classical definitions of "new" and

"recycled"production.[15]

In the second step, nitrite is oxidized to nitrate. In the oceans, this step is not as well understood as the

first, but thebacteriaNitrospinaandNitrobacterare known to carry out this step in the sea.[15]

Soil Conditions controlling nitrification rates

Substrate availability (presence of NH4+)

Aeration (availability of O2)

Well-drained soils with 60% soil moisture pH (near neutral)

Temperature (best 20-30C) => Nitrification is seasonal, affected by land use practices

See also

f-ratio

Haber process

Nitrifying bacteria

Nitrogen fixation

Simultaneous nitrification-denitrification

References

1. ^Nitrification Network. "Nitrification primer" (http://nitrificationnetwork.org/Introduction.php).

nitrificationnetwork.org. Oregon State University. Retrieved 21 August 2014.

2. ^ abcdHatzenpichler R. (2012) Diversity, physiology and niche differentiation of ammonia-oxidizing

archaea. Appl Environ Microbiol 78: 7501-7510

3. ^Treusch, A.H., Leininger, S., Kletzin, A., Schuster, S.C., Klenk, H.P., and Schleper, C. (2005) Novel

genesfor nitrite reductase and Amo-related proteins indicate a role of uncultivated mesophilic crenarchaeota in

nitrogen cycling. Environ Microbiol 7: 19851995

4. ^Purkhold, U., Pommerening-Roser, A., Juretschko, S.,Schmid, M.C., Koops, H.-P., and Wagner, M.

(2000) Phylogeny of all recognized species of ammonia oxidizers based on comparative 16S rRNA and amoA

sequence analysis: implications for molecular diversity surveys. Appl Environ Microbiol 66: 53685382

5. ^Martens-Habbena, W., Berube, P. M., Urakawa, H., de la Torre, J. R., Stahl, D. A. 2009. Ammoniaoxidation kinetics determine niche separation of nitrifying Archaea and Bacteria. Nature 461: 976-981.

6. ^Wuchter, C., Abbas, B., Coolen, M.J.L., Herfort, L., van Bleijswijk, J., Timmers, P., et al. (2006)

Archaeal nitrification in the ocean. Proc Natl Acad Sci USA 103: 1231712322.
http://nitrificationnetwork.org/Introduction.phphttp://en.wikipedia.org/wiki/Simultaneous_nitrification-denitrificationhttp://en.wikipedia.org/wiki/Nitrogen_fixationhttp://en.wikipedia.org/wiki/Nitrifying_bacteriahttp://en.wikipedia.org/wiki/Haber_processhttp://en.wikipedia.org/wiki/F-ratiohttp://en.wikipedia.org/wiki/Nitrobacterhttp://en.wikipedia.org/w/index.php?title=Nitrospina&action=edit&redlink=1http://en.wikipedia.org/wiki/F-ratiohttp://en.wikipedia.org/wiki/Water_columnhttp://en.wikipedia.org/wiki/Bacteriahttp://en.wikipedia.org/wiki/Primary_production


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External links

Nitrification at the heart of filtration (http://www.fishdoc.co.uk/filtration/nitrification.htm) at

fishdoc.co.uk

Nitrification (http://www.abdn.ac.uk/~mbi010/nitrification.htm) at University of Aberdeen

King's College

Nitrification Basics for Aerated Lagoon Operators (http://www.lagoonsonline.com/ripple.htm) at

lagoonsonline.com

Retrievedfrom "http://en.wikipedia.org/w/index.php?title=Nitrification&oldid=626932466"

Categories: Nitrogen metabolism Soil biology

Thispage was last modified on 24 September 2014 at 19:09.Textis available under the Creative Commons Attribution-ShareAlike License; additional termsmayapply. By using this site, you agree to the Terms of Use and Privacy Policy. Wikipedia is aregistered trademark of the Wikimedia Foundation, Inc., a non-profit organization.

7. ^Leininger, S., Urich, T., Schloter, M., Schwark, L., Qi, J., Nicol, G.W., Prosser, J.I., Schuster, S.C.,

Schleper, C. (2006) Archaea predominate among ammonia-oxidizing prokaryotes in soils. Nature 442:7014

pages806-9.

8. ^Marsh, K. L., G. K. Sims, and R. L. Mulvaney. 2005. Availability of urea to autotrophic ammonia-

oxidizing bacteria as related to the fate of 14C- and 15N-labeled urea added to soil. Biol. Fert. Soil. 42:137-

145.

9. ^Zhang, Y, Love, N, & Edwards, M (2009), "Nitrification in Drinking Water Systems", Critical Reviews inEnvironmental Science and Technology, 39(3):153-208, doi:10.1080/10643380701631739

(http://dx.doi.org/10.1080%2F10643380701631739).

10. ^McGuire, M.J., Lieu, N.I. and Pearthree, M.S. (1999). Using Chlorite Ion to Control Nitrification,

Journal American Water Works Association.91:10 (October) 52-61.

11. ^McGuire, M.J., Wu, X., Blute, N.K., Askenaizer, D., and Qin, G. (2009). Prevention of nitrification using

chlorite ion: Results of a demonstration project in Glendale, Calif., Journal American Water Works

Association.101:10 (October) 47-59.

12. ^Zehr, J. P. and R. M. Kudela. 2011. Nitrogen cycle of the open ocean: from genes to ecosystems. Annu.

Rev.Mar Sci. 3:197-225.

13. ^ abNitrification and Denitrification: Probing the Nitrogen Cycle in Aquatic Environments B. B. Ward

Microbial Ecology Vol. 32, No. 3 (1996), pp. 247-261

14. ^Hutchins, D. A., Mulholland, M. R., Fu, F. (2009). Nutrient cycles and marine microbes in a CO2-enriched

ocean.Oceanography. Vol. 22, pp. 128-145.

15. ^ abcZehr, J. P. and Kudela R. M.. 2011. Nitrogen cycle of the open ocean: from genes to ecosystems.

Annu.Rev. Mar Sci. 3:197-225.
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