Distribution of Nitrogen‐Fixation Genes in Prokaryotes Containing Alternative Nitrogenases

Abstract

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 (NifHD-KENB) 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 FeÀ S clusters during aerobic nitrogen fixation.

The electronic structure of FeV-cofactor in vanadium-dependent nitrogenase

“…5,14 Azotobacter vinelandii, the model organism used in the present work, produces all three different nitrogenase types, although under different physiological conditions, whereas most other nitrogen fixing organisms produce only one or two of the isoenzymes. 15,16 All three nitrogenase types are binary catalytic systems involving two participating component proteins. 17,18 One component is responsible for the nucleotide-dependent delivery of electrons to the other component, which provides the active site for substrate binding and reduction.…”

“…4,5,8,11,13 The MoFe protein is an  2  2 tetramer, encoded by the nifD and nifK genes, whereas the VFe protein and FeFe protein are  2  2  2 hexamers, respectively encoded by the vnfD, vnfK, vnfG and anfD, anfK, anfG genes. 4,5,16,19 MoFe protein, VFe protein and FeFe protein each contain two types of complex metallo-clusters. One of these is an [8Fe-7S] P-cluster common to all three systems and the other is an active site cofactor, specific to each system and respectively designated FeMo-cofactor, FeV-cofactor, and FeFe-cofactor.…”

Organic Materials and Their Chemically Extracted Humic and Fulvic Acids as Potential Soil Amendments for Faba Bean Cultivation in Soils with Varying CaCO3 Contents

“…Biological nitrogen fixation (BNF) is a key reaction of the nitrogen cycle [39], in which the nitrogenase enzyme is the dominant catalyst of dinitrogen reduction [40]. This enzyme changes N 2 to NH 3 [41,42].…”

Special Issue on Nitrogenases and Homologous Systems

“…Emphasizing the genetic and evolutionary aspects of this research area, Steven Mansoorabadi provides an overview of the members of the nitrogenase superfamily, Patricia Dos Santos gives a detailed account of alternative nitrogenases among microbes, and Sanfeng Chen discusses advances in transferring prokaryotic nitrogen‐fixation genes into non‐diazotrophic prokaryotic and eukaryotic hosts…”