Department of Biological Sciences, University of Alberta, Edmonton, AB, Canada.
Biochem Soc Trans. 2011 Dec;39(6):1826-31. doi: 10.1042/BST20110712.
Nitrous oxide, a potent greenhouse gas and ozone-depleting molecule, continues to accumulate in the atmosphere as a product of anthropogenic activities and land-use change. Nitrogen oxides are intermediates of nitrification and denitrification and are released as terminal products under conditions such as high nitrogen load and low oxygen tension among other factors. The rapid completion and public availability of microbial genome sequences has revealed a high level of enzymatic redundancy in pathways terminating in nitrogen oxide metabolites, with few enzymes involved in returning nitrogen oxides to dinitrogen. The aerobic methanotrophic bacteria are particularly useful for discovering and analysing diverse mechanisms for nitrogen oxide production, as these microbes both nitrify (oxidize ammonia to nitrite) and denitrify (reduce nitrate/nitrite to nitrous oxide via nitric oxide), and yet do not rely on these pathways for growth. The fact that methanotrophs have a rich inventory for nitrogen oxide metabolism is, in part, a consequence of their evolutionary relatedness to ammonia-oxidizing bacteria. Furthermore, the ability of individual methanotrophic taxa to resist toxic intermediates of nitrogen metabolism affects the relative abundance of nitrogen oxides released into the environment, the composition of their community, and the balance between nitrogen and methane cycling.
一氧化二氮是一种强效温室气体和消耗臭氧分子，作为人为活动和土地利用变化的产物继续在大气中积累。氮氧化物是硝化和反硝化的中间产物，在高氮负荷和低氧张力等条件下作为末端产物释放。微生物基因组序列的快速完成和公开可用性揭示了终止于氮氧化物代谢物的途径中存在高水平的酶冗余，只有少数酶参与将氮氧化物返回二氮。好氧甲烷营养细菌特别有助于发现和分析各种产生氮氧化物的机制，因为这些微生物既能硝化（将氨氧化为亚硝酸盐）又能反硝化（通过一氧化氮将硝酸盐/亚硝酸盐还原为一氧化二氮），但它们的生长并不依赖这些途径。甲烷营养菌具有丰富的氮氧化物代谢物库存，这在一定程度上是由于它们与氨氧化细菌的进化相关性。此外，个别甲烷营养分类群抵抗氮代谢有毒中间体的能力会影响释放到环境中的氮氧化物的相对丰度、其群落的组成以及氮和甲烷循环之间的平衡。
