Heterocyst Differentiation and Nitrogen Fixation in Cyanobacteria
Cyanobacteria face the difficult problem of fixing nitrogen while generating oxygen. Some solve this problem by storing carbohydrate during the day and using the stored material to fuel nitrogen fixation during the night. Others, notably Trichodesmium, a filamentous organism that is one of the major nitrogen fixers in the ocean, fixes only during the day, precisely at the same time that it is fixing CO2 and generating oxygen. How this is accomplished is still mysterious. There is no obvious morphological differentiation in Trichodesmium filaments. But there is now an acknowledged role for respiration in cyanobacterial photosynthesis, so possibly nitrogenase is protected by respiration in Trichodesmium. The heterocystous cyanobacteria, such as Anabaena, solve the problem of oxygen protection, at least in part, by differentiating specialized cells for nitrogen fixation at regular intervals along the filaments. We have been interested in the regulatory interactions among genes and their products, starting with the environmental cue of nitrogen depletion and concluding with a fully functional anaerobic factory for nitrogen fixation.
KeywordsAnabaena cyanobacteria gene expression green fluorescent protein heterocyst differentiation hetR gene spacing pattern
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