Nitrogen isotope fractionation during archaeal ammonia oxidation: coupled estimates from measurements of residual ammonium and accumulated nitrite

The naturally occurring nitrogen (N) isotopes, 15N and 14N, exhibit different reaction rates during many microbial N transformation processes, which results in N isotope fractionation. Such isotope effects are critical parameters for interpreting natural stable isotope abundances as proxies for biological process rates in the environment across scales. The kinetic isotope effect of ammonia oxidation (AO) to nitrite (NO2-), performed by ammonia-oxidizing archaea (AOA) and bacteria (AOB), is generally ascribed to the enzyme ammonia monooxygenase (AMO), which catalyzes the first step in this process. However, the kinetic isotope effect of AMO, or εAMO , has been typically determined based on isotope kinetics during product formation (cumulative product, NO2-) alone, which may have overestimated εAMO  due to possible accumulation of chemical intermediates and alternative sinks of ammonia/ammonium (NH3/NH4+). Here, we analyzed 15N isotope fractionation during archaeal ammonia oxidation based...

天然存在的氮（N）同位素15N与14N在诸多微生物氮转化过程中表现出不同的反应速率，从而导致氮同位素分馏（N isotope fractionation）。此类同位素效应是将自然丰度稳定同位素作为不同尺度环境中生物过程速率代用指标的关键参数。由氨氧化古菌（ammonia-oxidizing archaea, AOA）和氨氧化细菌（ammonia-oxidizing bacteria, AOB）介导的、将氨氧化（ammonia oxidation, AO）为亚硝酸盐（nitrite, NO2-）的动力学同位素效应，通常被归因于氨单加氧酶（ammonia monooxygenase, AMO）——该酶催化该过程的第一步反应。然而，以往对氨单加氧酶动力学同位素效应（εAMO）的测定，通常仅基于产物生成（累积产物亚硝酸盐NO2-）过程中的同位素动力学数据；由于化学中间体的潜在积累以及氨/铵（NH3/NH4+）的其他消耗途径，该方法可能高估了εAMO的数值。本研究基于……分析了古菌氨氧化过程中的15N同位素分馏。