Surveying N2O-Producing Pathways in Bacteria

Stein, Lisa Y.

doi:10.1016/b978-0-12-381294-0.00006-7

Cited by 176 publications

(174 citation statements)

References 60 publications

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“…The observation that NO binding accesses a shunt in the cyt P460 catalytic pathway provides evidence for the hypothesis that cyt P460 contributes to NO detoxification in the cell (11 (46). However, we suggest herein an alternative role in NH 2 OH detoxification through the production of N 2 O (vide supra) (11).…”

Section: Resultsmentioning

confidence: 98%

“…However, we suggest herein an alternative role in NH 2 OH detoxification through the production of N 2 O (vide supra) (11).…”

Section: Resultsmentioning

confidence: 99%

“…AOB possess machinery for nitrifier denitrification that reduces NO − 2 to N 2 O via a nitric oxide (NO) intermediate (11,12). The archetypal AOB Nitrosomonas europaea possesses genes for a Cucontaining nitrite reductase (NirK) and a membrane-bound, hemecontaining NO reductase (NorB).…”

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confidence: 99%

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Nitrosomonas europaea cytochrome P460 is a direct link between nitrification and nitrous oxide emission

Caranto

Vilbert

Lancaster

2016

Proc. Natl. Acad. Sci. U.S.A.

159

212

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Ammonia oxidizing bacteria (AOB) are major contributors to the emission of nitrous oxide (N 2 O). It has been proposed that N 2 O is produced by reduction of NO. Here, we report that the enzyme cytochrome (cyt) P460 from the AOB Nitrosomonas europaea converts hydroxylamine (NH 2 OH) quantitatively to N 2 O under anaerobic conditions. Previous literature reported that this enzyme oxidizes NH 2 OH to nitrite (NO − 2 ) under aerobic conditions. Although we observe NO − 2 formation under aerobic conditions, its concentration is not stoichiometric with the NH 2 OH concentration. By contrast, under anaerobic conditions, the enzyme uses 4 oxidizing equivalents (eq) to convert 2 eq of NH 2 OH to N 2 O. Enzyme kinetics coupled to UV/visible absorption and electron paramagnetic resonance (EPR) spectroscopies support a mechanism in which an Fe III -NH 2 OH adduct of cyt P460 is oxidized to an {FeNO} 6 unit. This species subsequently undergoes nucleophilic attack by a second equivalent of NH 2 OH, forming the N-N bond of N 2 O during a bimolecular, rate-determining step. We propose that NO − 2 results when nitric oxide (NO) dissociates from the {FeNO} 6 intermediate and reacts with dioxygen. Thus, NO − 2 is not a direct product of cyt P460 activity. We hypothesize that the cyt P460 oxidation of NH 2 OH contributes to NO and N 2 O emissions from nitrifying microorganisms. possesses a global warming potential nearly 300-fold greater than carbon dioxide (1). Atmospheric N 2 O concentrations have increased ∼120% since the preindustrial era, largely due to the widespread use of fertilizers required to produce sustenance for humans and livestock. N 2 O is a byproduct of the microbial metabolism of fertilizer components, including ammonia (NH 3 ) and nitrate (NO − 3 ); consequently, agricultural soils account for an estimated 60-75% of global N 2 O emissions. The metabolic pathway by which microorganisms oxidize NH 3 , nitrification, occurs in two phases, both of which are mediated by autotrophic microorganisms. In the first, NH 3 -oxidizing bacteria (AOB) or archaea (AOA) oxidize NH 3 to nitrite (NO − 2 ). In the second, NO − 2 is subsequently oxidized to NO − 3 by NO − 2 -oxidizing bacteria. NH 3 -oxidizing microbes contribute substantially to global N 2 O emissions, whereas NO − 2 -oxidizing bacteria produce negligible N 2 O (2, 3). AOB are proposed to emit N 2 O either as a byproduct of the nitrification pathway or as a product of the nitrifier denitrification pathway (i.e., the reduction of NO − 2 ) (4-6). Nitrification of NH 3 to NO − 2 occurs in two steps (7,8). The first step is catalyzed by NH 3 monooxygenase, which uses copper (Cu) and dioxygen (O 2 ) to hydroxylate NH 3 to hydroxylamine (NH 2 OH) (9). In AOB, the second step is thought to be the four-electron oxidation of NH 2 OH to NO − 2 by NH 2 OH oxidoreductase (HAO). HAO is a multiheme enzyme with eight c-type hemes per subunit: seven are electron transfer cofactors, and the eighth is the so-called P460 active site that contains a unique tyrosine cross-link to the ...

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Section: Resultsmentioning

confidence: 98%

“…However, we suggest herein an alternative role in NH 2 OH detoxification through the production of N 2 O (vide supra) (11).…”

Section: Resultsmentioning

confidence: 99%

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Nitrosomonas europaea cytochrome P460 is a direct link between nitrification and nitrous oxide emission

Caranto

Vilbert

Lancaster

2016

Proc. Natl. Acad. Sci. U.S.A.

159

212

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“…Recently, Vajrala et al (2013) found that NH 2 OH was an intermediate of ammonia oxidation in AOA, but they would not be able to produce N 2 O like AOB probably due to lack of genes for a homologue of hydroxylamine oxidoreductase (HAO) known to be responsible for N 2 O formation in AOB (Hooper and Terry 1979). In addition, AOA also lack genes encoding a potential NO-reductase (NOR), which is involved in nitrifier-denitrification and thus N 2 O production in AOB (Stein 2011;Tourna et al 2011). Therefore, we suggested that N 2 O emission from the two tested soil probably depended on denitrification by AOB.…”

Section: Discussionmentioning

confidence: 98%

“…Two mainly N 2 O-yielding can explain the reason for the higher N 2 O production by AOB than AOA, NH 2 OH oxidation and nitrifier denitrification (Shaw et al 2006;Stein 2011;Schreiber et al 2012). It was reported that N 2 O emission from the oxidation of NH 2 OH contributed very little to total N 2 O production and nitrifier denitrification was believed to be the predominant process for N 2 O production in soils with 50 % < WFPS < 70 % (Kool et al 2010(Kool et al , 2011.…”

Section: Discussionmentioning

confidence: 99%

Nitrogen fertiliser-induced changes in N2O emissions are attributed more to ammonia-oxidising bacteria rather than archaea as revealed using 1-octyne and acetylene inhibitors in two arable soils

et al. 2016

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Nitrification is believed to be one of the major sources of N 2 O production emitted from soil. Previous studies showed that both ammonia-oxidising bacteria (AOB) and archaea (AOA) can produce N 2 O via nitrification but their relative contributions are still poorly defined. Here, we used acetylene, an inhibitor of AOB and AOA ammonia monooxygenase (AMO), and 1-octyne, a selective inhibitor that specifically inhibits AOB AMO, to investigate how AOB versus AOA contribute to N 2 O emissions in two distinct arable soils. Soil amended with ammonium (NH 4 + ) increased N 2 O emissions to a greater extent than nitrate (NO 3 − ), and acetylene had a greater impact on N 2 O emissions in NH 4 + -treated soils than that in NO 3 − -amended soils, which indicated that nitrification was the dominant N 2 O emitting process in these two arable soils. In the alluvial and red soil, the percentage of evolved N 2 O after application of NH 4 + by AOB were 70.5~78.1 % and 18.7~19.7 % by AOA, respectively. Quantitative PCR revealed that NH 4 + addition stimulated AOB growth, and the growth could be significantly inhibited by acetylene or 1-octyne in the two soils. The stimulation of N 2 O emissions by NH 4 + and the relative suppression by inhibitors paralleled fluctuations in the AOB growth. In addition, cumulative N 2 O emissions were not correlated with AOA abundance in the two soils. Our results revealed that AOB could contribute more to soil N 2 O production than AOA in the NH 4 + -amended arable soils.

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Synthesis of Azoimidazolium Dyes with Nitrous Oxide

et al. 2014

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A new method for the synthesis of industrially important azoimidazolium dyes is presented. The procedure is based on a reagent which is rarely used in the context of synthetic organic chemistry: nitrous oxide (“laughing gas”). N2O is first coupled to N‐heterocyclic carbenes. Subsequent reaction with aromatic compounds through an AlCl3‐induced CH activation process provides azoimidazolium dyes in good yields.

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Surveying N2O-Producing Pathways in Bacteria

Cited by 176 publications

References 60 publications

Nitrosomonas europaea cytochrome P460 is a direct link between nitrification and nitrous oxide emission

Nitrosomonas europaea cytochrome P460 is a direct link between nitrification and nitrous oxide emission

Nitrogen fertiliser-induced changes in N2O emissions are attributed more to ammonia-oxidising bacteria rather than archaea as revealed using 1-octyne and acetylene inhibitors in two arable soils

Synthesis of Azoimidazolium Dyes with Nitrous Oxide

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