羟胺与氮循环：综述,Water Research

好氧铵氧化细菌最早是在100多年前分离出来的，而羟胺是已知的中间体。涉及羟胺转化为亚硝酸盐的酶促步骤仍在讨论中。长期以来，人们一直认为羟胺被羟胺氧化还原酶直接转化为亚硝酸盐。最近的酶学证据表明羟胺转化的实际产物是NO，而第三种酶（还未知）进一步将NO转化为亚硝酸盐。最近，分离并鉴定了氧化铵古细菌和完整的氧化铵细菌。这些微生物的中央氮代谢仍然给研究人员带来了同样的难题：羟胺如何转化为亚硝酸盐。氮的损失以NO和N 2的形式在所有三种类型的需氧铵氧化微生物中均已鉴定出O，并且已知羟胺在其形成中起着重要作用。然而，促进温室气体排放的途径和因素有待充分表征。羟胺在厌氧铵氧化细菌上也起着鲜为人知的作用，并且已知能抑制亚硝酸盐氧化细菌。在这篇综述中，讨论了这种难以捉摸的中间体在氮循环不同关键参与者代谢中的作用，以及羟胺作为关键氮代谢产物对于微生物群落和工程系统中微生物相互作用的推定重要性。总体而言，这是多年来第一次将所获得的有关羟胺和氮循环的知识进行汇总，

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Aerobic ammonium oxidizing bacteria were first isolated more than 100 years ago and hydroxylamine is known to be an intermediate. The enzymatic steps involving hydroxylamine conversion to nitrite are still under discussion. For a long time it was assumed that hydroxylamine was directly converted to nitrite by a hydroxylamine oxidoreductase. Recent enzymatic evidences suggest that the actual product of hydroxylamine conversion is NO and a third, yet unknown, enzyme further converts NO to nitrite. More recently, ammonium oxidizing archaea and complete ammonium oxidizing bacteria were isolated and identified. Still the central nitrogen metabolism of these microorganisms presents to researchers the same puzzle: how hydroxylamine is transformed to nitrite. Nitrogen losses in the form of NO and N2O have been identified in all three types of aerobic ammonium oxidizing microorganisms and hydroxylamine is known to play a significant role in the formation. Yet, the pathways and the factors promoting the greenhouse gas emissions are to be fully characterized. Hydroxylamine also plays a yet poorly understood role on anaerobic ammonium oxidizing bacteria and is known to inhibit nitrite oxidizing bacteria. In this review, the role of this elusive intermediate in the metabolism of different key players of the nitrogen cycle is discussed, as well as the putative importance of hydroxylamine as a key nitrogen metabolite for microbial interactions within microbial communities and engineered systems. Overall, for the first time putting together the acquired knowledge about hydroxylamine and the nitrogen cycle over the years in a review, setting potential hypothesis and highlighting possible next steps for research.