November 22, 2009
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		Nitrogenase Nitrogen fixation is catalyzed by the enzyme nitrogenase. Nitrogenase is composed of two multisubunit metalloproteins, called the molybdenum iron protein (Component 1) and the iron protein (Component 2). These are conventional nitrogenases. Alternative nitrogenases contain vanadium in Component 1 (alternative nitrogenases) or only iron (second alternative nitrogenases).Nitrogenase is likely to be an ancient enzyme, since it is distributed widely throughout Bacteria and Archaea. There are examples of possible or probably lateral gene transfer, but most of these likely occurred early in evolution. Both of the nitrogenase proteins are highly conserved, but the Fe protein, composed of two identical subunits encoded by nifH, is the most highly conserved. Nitrogenase phylogeny Nitrogenase genes are distributed throughout the prokaryotic kingdom, including representatives of the Archaea as well as the Eubacteria and Cyanobacteria. Although the phylogeny of nifH reflects the phylogeny of organisms based on ribosomal RNA genes, there are some differences. One deeply branching cluster is anomalous and is likely to represent an independent line of evolution, and includes some sequences from gram positive organisms, such as Clostridium. Since nitrogenase gene sequences do reflect phylogenetic affiliation, the sequence of nitrogenase genes can be used to identify the types of nitrogen-fixing microorganisms in different habitats. Nitrogenase Database Nitrogenase gene sequences have been sequenced in complete genomes, from genome libraries and amplified from individual organisms and the environment using the polymerase chain reaction. There are thousands of nitrogenase genes now in the public databases. We maintain an alignment of nifH genes in an ARB database. We have versions of this database, updated frequently available for download. Please be sure to read the documentation, which explains how sequences were chosen and aligned, and basic features of the publically distributed ARB nifH database.
University of California Santa Cruz Ocean Sciences Department Marine Microbiology Laboratory/Zehr Lab 1156 High Street, Santa Cruz, CA 95064 T: 831-459-3128 F: 831-459-4882