GENERAL MICROBIOLOGY - T.P. Pyrohiv - 2004

17. MOLECULAR NITROGEN FIXATION

17.3. BIOCHEMISTRY OF NITROGEN FIXATION

Nitrogen Fixation is carried out by an enzyme complex known as Nitrogenase. Nitrogenase consists of two components: a molybdenum-iron-sulfur protein and an iron-sulfur protein. Both the enzyme itself and the nitrogen fixation process are extremely sensitive to molecular oxygen. The fixation of nitrogen requires energy and reducing equivalents, which can be supplied via Photosynthesis, Respiration, or Fermentation.

In many Bacteria, nitrogenase is synthesized only when needed—that is, in the absence of a combined nitrogen source. Ammonium ions inhibit the synthesis of nitrogenase.

Nitrogen fixation is governed by the so-called nif genes. American scientists have constructed a bacterial plasmid incorporating all 17 known nif genes from the nitrogen-fixing bacterium Klebsiella pneumoniae. When this plasmid was transferred into Escherichia coli, the bacterium acquired The ability to fix nitrogen. French researchers successfully introduced the 17 nif genes into Yeast, which are eukaryotes and thus phylogenetically closer to plants than prokaryotes. However, the nif genes failed to fix nitrogen within the yeast Cell. Nevertheless, these studies provide optimism that introducing nitrogen-fixation genes into plants (primarily cereal crops) will ultimately be achieved.