Department of Chemistry, Wake Forest University, Winston-Salem, NC 27106, USA.
Chembiochem. 2020 Jun 15;21(12):1749-1759. doi: 10.1002/cbic.202000022. Epub 2020 Apr 16.
Biological nitrogen fixation is an inherent trait exclusive to a select number of prokaryotes. Although molybdenum nitrogenase is the dominant catalyst for dinitrogen reduction, some diazotrophs also contain one or two additional types of nitrogenase that use alternative metal content as the active-site cofactor. The occurrence of alternative nitrogenases has not been well studied due to the discriminatory expression of the molybdenum nitrogenase and lack of comprehensive genomic data. This study reports on the genomic analysis of 87 unique species containing alternative nitrogenase sequences. The distribution of nitrogen-fixing genes within these species from distinct taxonomic groups shows the presence of the minimum gene set required for nitrogen fixation, including catalytic and biosynthetic enzymes of the Mo-dependent system (NifHDKENB) and the varying occurrence of additional Nif-dedicated components. These include NifS and NifU, found primarily in aerobic species, thus suggesting that these genes are necessary to accommodate the high demand for Fe-S clusters during aerobic nitrogen fixation.
生物固氮是少数原核生物所具有的固有特性。尽管钼氮酶是二氮还原的主要催化剂，但一些固氮生物也含有一种或两种额外类型的氮酶，它们使用替代的金属含量作为活性位点辅因子。由于钼氮酶的选择性表达和缺乏全面的基因组数据，替代氮酶的发生尚未得到很好的研究。本研究报告了 87 个独特物种中含有替代氮酶序列的基因组分析。这些来自不同分类群的物种中固氮基因的分布表明存在固氮所需的最小基因集，包括 Mo 依赖性系统（NifHDKENB）的催化和生物合成酶以及额外的 Nif 专用成分的不同发生。这些包括主要存在于需氧物种中的 NifS 和 NifU，这表明这些基因对于适应需氧固氮过程中对 Fe-S 簇的高需求是必要的。
