nitrogen fixationmedical dictionary

<biochemistry> The incorporation of atmospheric nitrogen into ammonia by various bacteria, catalysed by nitrogenase.

This is an essential stage in the nitrogen cycle and is the ultimate source of all nitrogen in living organisms. In the sea, the main nitrogen fixers are Cyanobacteria.

There are several free living bacteria in soil that fix nitrogen including species of Azotobacter, Clostridium and Klebsiella. Rhizobium only fixes nitrogen when in symbiotic association, in root nodules, with leguminous plants. The oxygen sensitive nitrogenase is protected by plant produced leghaemoglobin and the plant obtains fixed nitrogen from the bacteria.

See: Frankia.

This entry appears with permission from the Dictionary of Cell and Molecular Biology

(11 Mar 2008)