Regulation of nitrogen fixation in heterocyst-forming cyanobacteria

Some cyanobacteria are able to reduce atmospheric dinitrogen to ammonia—a process where oxygen evolved by photosynthetic activity in the same cell is detrimental to nitrogen fixation. Strategies to avoid oxygen range from temporal separation of nitrogen fixation and oxygen evolution (in unicellular and filamentous, non-heterocystous strains) to spatial separation and cellular differentiation into nitrogen fixing heterocysts (in filamentous cyanobacteria). Recent research has begun to clarify the genes involved in nitrogen fixation, the mechanisms that regulate the expression of proteins involved in the assimilation of nitrogen from different sources and the way in which the cell is able to sense its nitrogen status.