title: Role of nitrite reductase in the ammonia-oxidizing pathway of Nitrosomonas europaea.
abstract: Metabolism of ammonia (NH(3)) and hydroxylamine (NH(2)OH) by wild-type and a nitrite reductase (nirK) deficient mutant of Nitrosomonas europaea was investigated to clarify the role of NirK in the NH(3) oxidation pathway. NirK-deficient N. europaea grew more slowly, consumed less NH(3), had a lower rate of nitrite (NO(2) (-)) production, and a significantly higher rate of nitrous oxide (N(2)O) production than the wild-type when incubated with NH(3) under high O(2) tension. In incubations with NH(3) under low O(2) tension, NirK-deficient N. europaea grew more slowly, but had only modest differences in NH(3) oxidation and product formation rates relative to the wild-type. In contrast, the nirK mutant oxidized NH(2)OH to NO(2) (-) at consistently slower rates than the wild-type, especially under low O(2) tension, and lost a significant pool of NH(2)OH-N to products other than NO(2) (-) and N(2)O. The rate of N(2)O production by the nirK mutant was ca. three times higher than the wild-type during hydrazine-dependent NO(2) (-) reduction under both high and low O(2) tension. Together, the results indicate that NirK activity supports growth of N. europaea by supporting the oxidation of NH(3) to NO(2) (-) via NH(2)OH, and stimulation of hydrazine-dependent NO(2) (-) reduction by NirK-deficient N. europaea indicated the presence of an alternative, enzymatic pathway for N(2)O production.
authors.affiliation: Department of Environmental Sciences, Geology 2207, University of California, Riverside, CA 92521, USA.
authors.forename: J Jason L
authors.initials: JJ
authors.lastname: Cantera
authors.forename: Lisa Y
authors.initials: LY
authors.lastname: Stein
mesh_terms: D000641:Ammonia / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D017353:Gene Deletion; D006834:Hydrazines / Q000378:metabolism; D019811:Hydroxylamine / Q000378:metabolism; D009572:Nitrite Reductases / Q000235:genetics / Q000378:metabolism*; D009573:Nitrites / Q000378:metabolism; D043370:Nitrosomonas europaea / Q000254:growth & development / Q000378:metabolism*; D009609:Nitrous Oxide / Q000378:metabolism; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D006834:Hydrazines; D009573:Nitrites; C029424:hydrazine; D019811:Hydroxylamine; D000641:Ammonia; D009572:Nitrite Reductases; D009609:Nitrous Oxide; D010100:Oxygen