Casciotti Karen L, Ward Bess B
Department of Geosciences, Princeton University, Princeton, NJ 08540, USA.
FEMS Microbiol Ecol. 2005 Apr 1;52(2):197-205. doi: 10.1016/j.femsec.2004.11.002. Epub 2004 Dec 8.
Nitric oxide (NO) and nitrous oxide (N2O) are climatically important trace gases that are produced by both nitrifying and denitrifying bacteria. In the denitrification pathway, N2O is produced from nitric oxide (NO) by the enzyme nitric oxide reductase (NOR). The ammonia-oxidizing bacterium Nitrosomonas europaea also possesses a functional nitric oxide reductase, which was shown recently to serve a unique function. In this study, sequences homologous to the large subunit of nitric oxide reductase (norB) were obtained from eight additional strains of ammonia-oxidizing bacteria, including Nitrosomonas and Nitrosococcus species (i.e., both beta- and gamma-Proteobacterial ammonia oxidizers), showing widespread occurrence of a norB homologue in ammonia-oxidizing bacteria. However, despite efforts to detect norB homologues from Nitrosospira strains, sequences have not yet been obtained. Phylogenetic analysis placed nitrifier norB homologues in a subcluster, distinct from denitrifier sequences. The similarities and differences of these sequences highlight the need to understand the variety of metabolisms represented within a "functional group" defined by the presence of a single homologous gene. These results expand the database of norB homologue sequences in nitrifying bacteria.
一氧化氮（NO）和一氧化二氮（N₂O）是对气候有重要影响的痕量气体，由硝化细菌和反硝化细菌产生。在反硝化途径中，一氧化氮还原酶（NOR）可将一氧化氮（NO）转化为一氧化二氮（N₂O）。氨氧化细菌欧洲亚硝化单胞菌也拥有一种功能性一氧化氮还原酶，最近的研究表明它具有独特的功能。在本研究中，从另外8株氨氧化细菌中获得了与一氧化氮还原酶大亚基（norB）同源的序列，这些细菌包括亚硝化单胞菌属和亚硝化球菌属的细菌（即β-和γ-变形菌纲的氨氧化菌），这表明氨氧化细菌中普遍存在norB同源物。然而，尽管努力从亚硝化螺菌属菌株中检测norB同源物，但尚未获得相关序列。系统发育分析将硝化细菌的norB同源物置于一个亚簇中，与反硝化细菌的序列不同。这些序列的异同突出了理解由单个同源基因定义的“功能组”中所代表的各种代谢的必要性。这些结果扩展了硝化细菌中norB同源物序列的数据库。
