Nitrogen Fixation in Cyanobacteria

Lucas J Stal, Netherlands Institute of Ecology, Yerseke, The Netherlands

Published online: July 2008

DOI: 10.1002/9780470015902.a0021159

Cyanobacteria are oxygenic photosynthetic bacteria that are widespread in marine, freshwater and terrestrial environments and many of them are capable of fixing atmospheric nitrogen. But ironically, nitrogenase, the enzyme that is responsible for the reduction of N2, is extremely sensitive to O2. Therefore, oxygenic photosynthesis and N2 fixation are not compatible. Hence, cyanobacteria had to evolve a variety of strategies circumventing this paradox allowing them to grow at the expense of N2, a ubiquitous source of nitrogen.

Keywords: circadian rhythm; cyanobacteria; heterocyst; nitrogenase; nitrogen fixation

Figure 1. Examples of N2-fixing cyanobacteria. Top: heterocystous cyanobacteria. From left to right: Calothrix, Fischerella and Nodularia. Center: nonheterocystous filamentous cyanobacteria. From left to right: Trichodesmium, Symploca and Lyngbya. Bottom: unicellular cyanobacteria. From left to right: Crocosphaera, Cyanothece and Gloeothece.
Figure 2. Nitrogenase is an enzyme complex consisting of dinitrogenase reductase (Fe-protein), composed of two identical subunits encoded by nifH, and dinitrogenase (MoFe-protein), composed of four subunits, 2 by 2 identical and encoded by nifD and nifK. Dinitrogenase reductase reduces dinitrogenase after accepting electrons from ferredoxin, while hydrolyzing ATP. Dinitrogenase subsequently reduces N2 to NH3 and H2.
Figure 3. Daily patterns of N2 fixation in various cyanobacteria. Top: heterocystous cyanobacteria. From left to right: Anabaena, Aphanizomenon and Nodularia. Center: nonheterocystous filamentous cyanobacteria. From left to right: Trichodesmium, Symploca and Lyngbya. Bottom: unicellular cyanobacteria. From left to right: Gloeothece, Crocosphaera and Cyanothece.
Figure 4. A heterocyst neighboured by vegetative cells. This scheme illustrates the spatial separation of oxygenic photosynthesis (in the vegetative cell) and N2 fixation (in the heterocyst) and the relationships between them.
Figure 5. N2 fixation is monitored in an exponentially growing culture of Lyngbya aestuarii. Nitrogenase activity shows a cycle of approximately 24 h, indicative for a circadian rhythm. Reproduced from Stal LJ (1985) Nitrogenase activity in the non-heterocystous cyanobacterium Oscillatoria sp. grown under alternating light-dark cycles. Archives of Microbiology 143: 67–71. Figure 1, with kind permission from Springer Science and Business Media.
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 Further Reading
    Bergman B, Gallon JR, Rai AN and Stal LJ (1997) N2 fixation by non-heterocystous cyanobacteria. FEMS Microbiology Reviews 19: 139–185.
    Berman-Frank I, Lundgren P and Falkowski P (2003) Nitrogen fixation and photosynthetic oxygen evolution in cyanobacteria. Research in Microbiology 154: 157–164.
    Fay P (1992) Oxygen relations of nitrogen fixation in cyanobacteria. Microbiological Reviews 56: 340–373.
    Gallon JR (1992) Reconciling the incompatible: N2 fixation and O2. New Phytologist 122: 571–609.
    Sherman LA, Meunier P and Colón-López MS (1998) Diurnal rhythms in metabolism: a day in the life of a unicellular, diazotrophic cyanobacterium. Photosynthesis Research 58: 25–42.
    book Stal LJ and Zehr JP (2008) "Cyanobacterial nitrogen fixation in the ocean: diversity, regulation, and ecology". In: Flores E and Herrero A (eds) The Cyanobacteria: Molecular Biology, Genomics and Evolution, pp 423–446. Norfolk, UK: Caister Academic Press.

Related Sub-Topics:

Bacteria | Algae | Biosynthesis
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Article Title: Nitrogen Fixation in Cyanobacteria
 
How to Cite close
Stal, Lucas J(Jul 2008) Nitrogen Fixation in Cyanobacteria. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0021159]