noun, plural: nif genes
The nif genes are genes involved in nitrogen fixation. They are found in nitrogen-fixing bacteria. They occur as an operon in free-living anaerobic nitrogen-fixing bacteria such as Klebsiella pneumoniae, Rhodospirillum rubrum, and Rhodobacter capsulatus. These genes may also be found on plasmids (together with the other genes, e.g. nod genes) in symbiotic bacteria, such as in Rhizobium inhabiting the roots of leguminous plants.
The nif genes code for proteins essential in nitrogen fixation, such as nitrogenase and certain regulatory proteins. NifA protein regulated the nif genes transcription. NifA protein is in turn regulated by NtrC. The expression of NifA protein is triggered when fixed nitrogen and oxygen levels are low. In contrast, a sufficient concentration of nitrogen or oxygen would stimulate the protein NifL. The latter inhibits the activity of NifA and this inhibits the formation of nitrogenase.
Nitrogen fixation is important because many living organisms are unable to metabolize directly the atmospheric nitrogen and would require the nitrogen fixation capability of certain bacteria in order to produce a form of nitrogen (e.g. ammonia) that can be readily utilized.