Nitrogen fixation in bacteria

An important property of many cyanobacteria is their ability to fix atmospheric (molecular) nitrogen. This process depends on the enzyme nitrogenase. This enzyme can function only under anaerobic conditions. It has been suggested that the metabolism of cyanobacteria functions best at low O2 concentrations because these organisms are relics of nearly two billion years of evolution under conditions of the oxygen-poor earth s atmosphere.  

Biological systems that participate in nitrogen fixation contain a composite metal-requiring enzyme system which assures a source of electrons of high reductive efficiency, and another enzyme which makes use of these electrons to reduce N2 to NH4  

Biological nitrogen fixation is then followed by nitrification NH4+ + 2O2 NO3- + H2O + 2H+ 

Fritz Haber, 1968-1934, German physical chemist, winner of the Nobel Prize for chemistry in 1918 for the synthesis of ammonia from its elements. With Carl Bosch, he invented a process for the large scale production of ammonia for nitrogen fertilizers. 

Carl Bosch, 1874-1940, German industrial chemist, developed the Haber-Bosch process for high-pressure synthesis of ammonia. Bosch shared with Friedrich Bergius the 1931 Nobel Prize for chemistry for their contribution to the invention and development of chemical high pressure methods.  

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Bums, R. C. and Hardy, R. W. F. (1975). "Nitrogen Fixation in Bacteria and Higher Plants." Springer-Verlag, New York. 

Nevertheless, cereal plants can interact with endosymbionts, capable of nitrogen fixation in other species, and be stimulated in their productivity. The odds of soil life are balanced for some bacteria by their interactivity at rhizosphere level, and a realm of exchanged signals dictates entry into hormonally reprogrammed root sites. Specificity for partner plant species is part of a fine speciation process that actively involves the bacterial nodulation genes, and continues to drive their variation dynamics. 

Bohme, H. (1998) Regulation of nitrogen fixation in heterocyst forming bacteria. Trends Plant Sci., 3, 346-51. 

Bacterial ferredoxins function primarily as electron carriers in ferredoxin-mediated oxidation reduction reactions. Some examples are reduction of NAD, NADP, FMN, FAD, sulfite and protons in anaerobic bacteria, CO -fixation cycles in photosynthetic bacteria, nitrogen fixation in anaerobic nitrogen fixing bacteria, and reductive carboxylation of substrates in fermentative bacteria. The roles of bacterial ferredoxins in these reactions have been summarized by Orme-Johnson (2), Buchanan and Arnon (3), and Mortenson and Nakos (31). 

Fogg, G. E. (1978). Nitrogen fixation in the oceans. In Environmental role of Nitrogen-fixing Blue-green Algae and Asymbiotic Bacteria. Ecol. Bull. (Granhall, U., ed.), Vol. 26. Swedish Natural Science Research Council, Stockholm, pp. 11—19. 

Welsh, D. T. (2000). Nitrogen fixation in seagrass meadows Regulation, plant-bacteria interactions and significance to primary productivity. Ecol. Lett. 3(1), 58—71. 

Nitrogen fixation in the marine environment occurs in benthic (sediments and microbial mats) and pelagic environments, and in salt marsh soils (see Carpenter and Capone, Chapter 4, this volume). Since very diverse microorganisms that span the Bacteria and Archaea domains of life can fix nitrogen, it is often difficult to ascertain which organisms are responsible for observed nitrogen fixation rates. Our discussion of the application of molecular approaches to the study of marine nitrogen fixation is brief because it has been reviewed extensively elsewhere (Carpenter and Capone, Chapter 4, this volume Foster and O MuUan Chapter 27, this volume Scanlan and Post, Chapter 24, this volume Paerl and Zehr, 2000 Zehr and Ward, 2002 Zehr et al., 2003). 

Classifying Nitrogen fixation in the soil is accomplished by bacteria living in the roots of certain plants. Name some of these plants. 

Fauque G, LeGall J, Barton LL (1991) Sulfate-reducing and sulfur-reducing bacteria. In Shively JM, Barton LL (eds) Variations in autotrophic life. Academic Press, London, pp 271-337 Fay P (1992) Oxygen relations of nitrogen fixation in cyanobacteria. Microbiol Rev 56 340-373... 

Free-living bacteria in Temperate Zones fix only 2 to 3 kg N ha yr In the tropics, however, there is increasing evidence that nitrogen fixation by bacteria, particularly those growing in associative symbioses may be important. In Brazil, the nitrogen-fixing bacterium Azotobacter paspali lives in association with roots of the tropical forage plant Paspalum notatum. This association fixes 90 kg N ha yr [29]. 

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