High nitrous oxide isotopic variability during denitrification by Pseudomonas species bearing NirK and NirS

作者：Noémy Chénier, Paul Magyar, Jakob Zopfi, Claudia Frey, Moritz F. Lehmann, Joachim Mohn · 发表于：Zenodo (CERN European Organization for Nuclear Research) · 年份：2026 · DOI：10.5281/zenodo.21534018 · 研究领域：Chemistry、Environmental chemistry、Inorganic chemistry

Nitrous oxide (N₂O) isotopocules provide key insights into microbial nitrogen cycling, but their interpretation requires well-constrained values for both oxygen isotope signatures (δ¹⁸O–N₂O) and intramolecular ¹⁵N site preference (SP) associated with N₂O production pathways. Site preference is widely used to distinguish N₂O formation pathways because bacterial denitrification is generally assumed to yield SP values near 0 ‰ through canonical NorB-mediated NO reduction. However, the extent to which SP remains stable across physiological states and changing NO reduction pathways remains poorly constrained. Likewise, interpretation of δ¹⁸O–N₂O associated with denitrification requires understanding the relative contributions of branching kinetic isotope effects and oxygen atom exchange between nitrite and water during N₂O formation. Here, we investigated N₂O isotopic signatures during denitrification by Pseudomonas aureofaciens (NirK-bearing) and Pseudomonas chlororaphis (NirS-bearing) under active-growth and resuspension conditions using quantum cascade laser absorption spectroscopy (QCLAS) and isotope ratio mass spectrometry (IRMS). SP tracked canonical NorB-mediated NO reduction but transiently increased above +10 ‰ during early N₂O production, suggesting temporary activity of alternative NO reductases. These dynamics were only resolved through continuous QCLAS measurements, highlighting the importance of time-resolved isotopic observations. While SP remains a useful indicator...