Nitrogen fixation in filamentous cyanobacteria
Cyanobacteria have the same requirements for nitrogen fixation as other diazotrophs: synthesis of the nitrogenase complex and its cofactors, a source of ATP and low potential electrons, and an environment protected from oxygen. Unique among diazotrophs, cyanobacteria evolve oxygen in the light. Filamentous strains such as Anabaena solve the problem of protecting nitrogenase from oxygen by differentiating specialized cells called heterocysts at regular intervals along the filament. In the heterocyst, the oxygen-evolving reaction of Photosystem II is turned off, CO2 fixation stops, nitrogenase, cofactors and electron donor proteins are synthesized, and the oxidative pentose pathway is activated. A double-layered envelope of polysaccharide and glycolipid is laid down outside the existing cell wall. New connections between the heterocyst and the adjacent vegetative cells are established; these mediate the transport of carbohydrate and of fixed nitrogen.
KeywordsNitrogen Fixation Shuttle Vector Heterocyst Differentiation Wild Type Anabaena Amino Terminal Half
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