Abiotic Conversion of Extracellular NH2OH Contributes to N2O Emission during Ammonia Oxidation

Shurong Liu (Corresponding Author), Ping Han, Linda Hink, James I. Prosser, Michael Wagner, Nicolas Bruggemann

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Abiotic processes involving the reactive ammonia-oxidation intermediates nitric oxide (NO) or hydroxylamine (NH2OH) for N2O production has been indicated recently. The latter process would require the availability of substantial amounts of free NH2OH for chemical reactions during ammonia (NH3) oxidation, but little is known about extracellular NH2OH formation by the different clades of ammonia-oxidizing microbes. Here we determined extracellular NH2OH concentrations in culture media of several ammonia-oxidizing bacteria (AOB) and archaea (AOA), as well as one complete ammonia oxidizer (comammox) enrichment (Ca. Nitrospira inopinata) during incubation under standard cultivation conditions. NH2OH was measurable in the incubation media of Nitrosomonas europaea, Nitrosospira multiformis, Nitrososphaera gargensis, and Ca. Nitrosotenuis uzonensis, but not in media of the other tested AOB and AOA. NH2OH was also formed by the comammox enrichment during NH3 oxidation. This enrichment exhibited the largest NH2OH:final product ratio (1.92%), followed by N. multiformis (0.56%) and N. gargensis (0.46%). The maximum proportions of NH4+ converted to N2O via extracellular NH2OH during incubation, estimated on the basis of NH2OH abiotic conversion rates, were 0.12%, 0.08% and 0.14% for AOB, AOA and Ca. Nitrospira inopinata, respectively, and were consistent with published NH4+:N2O conversion ratios for AOB and AOA.

Original languageEnglish
Pages (from-to)13122–13132
Number of pages11
JournalEnvironmental Science & Technology
Issue number22
Early online date17 Oct 2017
Publication statusPublished - 21 Nov 2017

Bibliographical note

The authors wish to thank Holger Wissel for his assistance with 15N isotope analysis, Franz Leistner for his assistance in gas chromatography and Kerim Dimitri Kits for helpful discussions. We would like to thank Andreas Pommerening-Röser (University of Hamburg, Germany) for providing us with AOB strains. SL was supported by the Chinese Scholarship Council (scholarship no. 201206760007). MW and PH were supported by an ERC Advanced Grant (NITRICARE, 294343). LH is funded through the Nitrous Oxide Research Alliance (NORA), a Marie Skłodowska-Curie ITN and research project under the EU's seventh framework program (FP7).


  • Journal Article
  • hydroxylamine
  • greenhouse gas
  • biotic-abiotic
  • N2O formation mechanism
  • ammonia oxidizer
  • reactive N
  • comammox


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