好氧氨氧化过程中的关键酶及N2O排放研究进展

氧化亚氮(nitrous oxide, N₂O)排放量的持续增加对全球生态平衡造成了严重的威胁。微生物N₂O排放占主要来源。其中,好氧氨氧化过程是氨在有氧的条件下氧化为亚硝酸盐,其直接或间接地影响着全球产生N₂O与释放量。氨氧化古菌(ammonia-oxidizing archaea, AOA)、氨氧化细菌(ammonia-oxidizing bacteria, AOB)、全程氨氧化菌(complete ammonia oxidization, Comammox)和异养氨氧化菌(heterotrophic ammonium oxidizing bacteria, HAOB)是氨氧化过程中主要的参与者,明确这四类微生物N₂O产生的机制对缓解全球N₂O排放是必要的。本文综述了AOA、AOB、Comammox和HAOB在好氧氨氧化过程中驱动的N₂O产生途径,并结合酶学分析了一些关键酶在N₂O产生途径中的作用。本文旨在为调控生物N₂O排放提供理论基础。

Key enzymes and N2O emission in aerobic ammonia oxidation process

The increasing emission of nitrous oxide (N₂O) poses a serious threat to global ecological balance, to which microbes contribute a lot. Aerobic ammonia oxidation is the oxidation of ammonia to nitrite under aerobic conditions, which directly or indirectly affects the global production and release of N₂O. Ammonia-oxidizing archaea (AOA), ammonia-oxidizing bacteria (AOB), complete ammonia oxidizers (Comammox), and heterotrophic ammonia-oxidizing bacteria (HAOB) are major contributors to ammonia oxidation. It is important for the mitigation of N₂O emission to clarify how N₂O is produced by the four types of microorganisms. This paper reviewed the N₂O production pathways in AOA, AOB, Comammox and HAOB driven by the aerobic ammonia oxidation process. The roles of some key enzymes in the N₂O production pathways were elucidated through enzymatic analysis. Ammonia monooxygenase (AMO) is the first key enzyme in the autotrophic aerobic ammonia oxidation process, and the direct product of hydroxylamine oxidation is NO instead of NO₂^-, which is then converted to NO₂^- by an unknown enzyme. The aerobic ammonia oxidation process and related enzymes of HAOB are not completely clear, and the issue of N₂O emission needs to be further studied. This paper aims to lay a theoretical basis for regulating biological N₂O emission.