Kobayashi Kanae, Nishina Kazuya, Fukushima Keitaro, Onishi Yuji, Makabe Akiko, Oshiki Mamoru, Koba Keisuke, Okabe Satoshi
Division of Environmental Engineering, Faculty of Engineering, Hokkaido University, Sapporo, Hokkaido 060-8628, Japan.
Institute for Extra-cutting-edge Science and Technology Avant-garde Research (X-star), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka 237-0061, Japan.
ISME J. 2025 Jan 2;19(1). doi: 10.1093/ismejo/wraf115.
Analysing the nitrogen (15ε) and oxygen (18ε) isotope effects of anaerobic ammonium oxidation (anammox) is essential for accurately assessing its potential contribution to fixed-N losses in the ocean, yet the 18ε of anammox remains unexplored. Here, we determined the previously unexplored 18ε of anammox using a highly enriched culture of the marine anammox species "Ca. Scalindua sp". Because Scalindua significantly accelerated oxygen isotope exchange between NO2- and H2O, we introduced a new rate constant for anammox-mediated oxygen isotope exchange (keq, AMX = 8.44 ~ 13.56 × 10-2 h-1), which is substantially faster than abiotic oxygen isotope exchange (keq, abio = 1.13 × 10-2 h-1), into a numerical model to estimate the 18ε during anammox. Based on our experimental results, we successfully determined the 18ε associated with: (1) conversion of NO2- to N2 (18εNO2- → N2 = 10.6 ~ 16.1‰), (2) NO2- oxidation to NO3- (18εNO2- → NO3- = -2.9 ~ -11.0‰, inverse fractionation), (3) incorporation of oxygen from water during NO2- oxidation to NO3- (18εH2O = 16.4 ~ 19.2‰). Our study underscores the possibility that unique anammox oxygen isotope signals may be masked due to substantial anammox-mediated oxygen isotope exchange between NO2- and H2O. Therefore, careful consideration is required when utilizing δ18ONO3- and δ18ONO2- as geochemical markers to assess the potential contribution of anammox to fixed-N losses in the ocean.
分析厌氧氨氧化（anammox）过程中氮（15ε）和氧（18ε）的同位素效应对于准确评估其对海洋中固定氮损失的潜在贡献至关重要，然而anammox的18ε仍未得到探索。在此，我们使用海洋anammox物种“Ca. Scalindua sp”的高度富集培养物确定了此前未被探索的anammox的18ε。由于Scalindua显著加速了NO2-与H2O之间的氧同位素交换，我们将一个新的anammox介导的氧同位素交换速率常数（keq, AMX = 8.44 ~ 13.56×10-2 h-1，其比非生物氧同位素交换速率常数（keq, abio = 1.13×10-2 h-1）快得多）引入一个数值模型来估算anammox过程中的18ε。基于我们的实验结果，我们成功确定了与以下过程相关的18ε：（1）NO2-转化为N2（18εNO2- → N2 = 10.6 ~ 16.1‰），（2）NO2-氧化为NO3-（18εNO2- → NO3- = -2.9 ~ -11.0‰，逆向分馏），（3）NO2-氧化为NO3-过程中水中氧的掺入（18εH2O = 16.4 ~ 19.2‰）。我们的研究强调了由于anammox介导的NO2-与H2O之间大量的氧同位素交换，独特的anammox氧同位素信号可能被掩盖的可能性。因此，在利用δ18ONO3-和δ18ONO2-作为地球化学标记来评估anammox对海洋中固定氮损失的潜在贡献时，需要谨慎考虑。
