This view shows enzymes only for those organisms listed below, in the list of taxa known to possess the pathway. If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
|Superclasses:||Generation of Precursor Metabolites and Energy → Chemoautotrophic Energy Metabolism|
|Generation of Precursor Metabolites and Energy → Electron Transfer|
Some taxa known to possess this pathway include : Nitrobacter, Nitrobacter alkalicus, Nitrobacter hamburgensis, Nitrobacter vulgaris, Nitrobacter winogradskyi, Nitrococcus, Nitrospina, Nitrospira moscoviensis
Nitrification, the oxidation of ammonia to nitrate by microorganisms, is a key process in the global nitrogen cycle, resulting in nitrogen loss from ecosystems, eutrophication of surface and ground waters, and the production of atmospherically active trace gases. No known bacteria are capable of carrying out the whole process. Rather, ammonia oxidizers convert ammonia to nitrite (see ammonia oxidation I (aerobic)), while nitrite oxidizers oxidize nitrite to nitrate.
The facultative chemolithotroph
Nitrobacter is considered the dominant nitrite oxidizer in freshwater and terrestrial ecosystems, and four species are known:
Nitrobacter vulgaris and
Nitrobacter alkalicus. The other three genera are obligate lithoautotrophs, and have been isolated mostly from marine environments, although
Nitrospira moscoviensis is a fresh water organism, isolated from a coroded iron pipe.
The key enzyme of nitrite oxidation is nitrite oxidoreductase (NOR), which catalyzes the conversion of nitrite to nitrate in all of the nitrite oxidizers. The enzyme is an iron-sulfur molybdoprotein, and nitrite is transformed at the molybdenum center by a two electron transfer, generating nitrate and molybdenum (IV). Under unaerobic conditions the enzyme is a nitrate reductase, catalyzing the reverse reaction [Meincke92]. The electrons that are released from the nitrite oxidoreductase complex are subsequently transferred to cytochrome c oxidase through several forms of cytochrome c550 [Yamanaka88]. Both soluble and membrane-bound class IA/B cytochrome c-550 proteins were purified and shown to be electron donors for theoxidase [Tanaka82, Nomoto93].
Ehrich95: Ehrich S, Behrens D, Lebedeva E, Ludwig W, Bock E (1995). "A new obligately chemolithoautotrophic, nitrite-oxidizing bacterium, Nitrospira moscoviensis sp. nov. and its phylogenetic relationship." Arch Microbiol 164(1);16-23. PMID: 7646315
Juretschko98: Juretschko S, Timmermann G, Schmid M, Schleifer KH, Pommerening-Roser A, Koops HP, Wagner M (1998). "Combined molecular and conventional analyses of nitrifying bacterium diversity in activated sludge: Nitrosococcus mobilis and Nitrospira-like bacteria as dominant populations." Appl Environ Microbiol 1998;64(8);3042-51. PMID: 9687471
Nomoto93: Nomoto T, Fukumori Y, Yamanaka T (1993). "Membrane-bound cytochrome c is an alternative electron donor for cytochrome aa3 in Nitrobacter winogradskyi." J Bacteriol 175(14);4400-4. PMID: 8392510
Schramm98: Schramm A, De Beer D, Wagner M, Amann R (1998). "Identification and activities in situ of Nitrosospira and Nitrospira spp. as dominant populations in a nitrifying fluidized bed reactor." Appl Environ Microbiol 1998;64(9);3480-5. PMID: 9726900
Watson71: Watson SW, Waterbury JB "Characteristics of two marine nitrite oxidizing bacteria, Nitrospina gracilis, new genus new species, and Nitrococcus, new genus new species." Archiv. Mikrobiol. 1971;77(3):203-230.
Aamand96: Aamand J, Ahl T, Spieck E (1996). "Monoclonal antibodies recognizing nitrite oxidoreductase of Nitrobacter hamburgensis, N. winogradskyi, and N. vulgaris." Appl Environ Microbiol 1996;62(7);2352-5. PMID: 8779572
Kirstein93: Kirstein K, Bock E (1993). "Close genetic relationship between Nitrobacter hamburgensis nitrite oxidoreductase and Escherichia coli nitrate reductases." Arch Microbiol 160(6);447-53. PMID: 8297210
Maron03: Maron PA, Coeur C, Pink C, Clays-Josserand A, Lensi R, Richaume A, Potier P (2003). "Use of polyclonal antibodies to detect and quantify the NOR protein of nitrite oxidizers in complex environments." J Microbiol Methods 53(1);87-95. PMID: 12609727
OKelley70: O'Kelley JC, Becker GE, Nason A (1970). "Characterization of the particulate nitrite oxidase and its component activities from the chemoautotroph Nitrobacter agilis." Biochim Biophys Acta 205(3);409-25. PMID: 4394298
Spieck98: Spieck E, Ehrich S, Aamand J, Bock E (1998). "Isolation and immunocytochemical location of the nitrite-oxidizing system in nitrospira moscoviensis." Arch Microbiol 169(3);225-30. PMID: 9477257
Starkenburg06: Starkenburg SR, Chain PS, Sayavedra-Soto LA, Hauser L, Land ML, Larimer FW, Malfatti SA, Klotz MG, Bottomley PJ, Arp DJ, Hickey WJ (2006). "Genome sequence of the chemolithoautotrophic nitrite-oxidizing bacterium Nitrobacter winogradskyi Nb-255." Appl Environ Microbiol 72(3);2050-63. PMID: 16517654
SundermeyerKlin84: Sundermeyer-Klinger, H., Meyer, W., Warninghoff, B., Bock, E. "Membrane-bound nitrite oxidoreductase of Nitrobacter: evidence for a nitrate reductase system." Arch. Microbiol. 1984;140:153-158.
Tanaka83: Tanaka, Y., Fukumori, Y., Yamanaka, T. "Purification of cytochrome a1c1 from Nitrobacter agilis and characterization of nitrite oxidationsystem of the bacterium." Arch. Microbiol. 1983;135:265-271.
Yamanaka81: Yamanaka T, Kamita Y, Fukumori Y (1981). "Molecular and enzymatic properties of "cytochrome aa3"-type terminal oxidase derived from Nitrobacter agilis." J Biochem (Tokyo) 89(1);265-73. PMID: 6260762
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