nitrogen fixation(redirected from nitrogen-fixer)
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Related to nitrogen-fixer: nitrogen cycle
process in which atmospheric nitrogen is converted to ammonia.
Farlex Partner Medical Dictionary © Farlex 2012
1. The conversion of atmospheric nitrogen into compounds, such as ammonia, by natural agencies or various industrial processes.
2. The conversion by certain soil microorganisms, such as rhizobia, of atmospheric nitrogen into compounds that plants and other organisms can assimilate.
ni′tro·gen-fix′er (-fĭk′sər) n.
The American Heritage® Medical Dictionary Copyright © 2007, 2004 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.
nitrogen fixationthe utilization of atmospheric nitrogen in the synthesis of AMINO ACIDS by some bacteria. Such bacteria can be free-living (e.g. Azotobacter, an aerobe; Clostridium, an obligate anaerobe) while others (e.g. Rhizobium) live in association with plants, occupying swellings in the root called root nodules. The latter relationship is one of SYMBIOSIS, in that the plant gains nutrients and thus can live in nitrogen-poor soils, while the nitrogen-fixer obtains a supply of carbohydrates from the plant. The nitrogen is reduced to ammonia in the microbes by action of the enzyme nitrogenase: N2 + 3 H2 → 2 NH3, the ammonia then reacting with keto acids to form amino acids.
Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005