Heterocyst and akinete differentiation in cyanobacteria: a view toward cyanobacterial symbiosis

Abstract Cyanobacteria are an ancient, phylogenetically coherent group of organisms characterized by oxygenic photosynthesis. They have evolved several differentiated cell variants that include heterocysts and akinetes to perform specialized functions. Heterocyst pattern formation represents one of the earliest multicellular patterning processes in the history of life. The structure and metabolic activity serve to spatially separate the oxygen-sensitive process of nitrogen fixation from oxygen-producing photosynthesis in vegetative cells. Germination of akinetes of filamentous heterocyst-forming cyanobacteria of the order Nostocales is a crucial process that ensures survival during stress conditions. The current chapter focuses on morphological and structural variation in heterocyst and akinete composition with emphasis on gene regulation for the differentiation process and their metabolism. The ability to form symbiotic associations with different organisms revealing the versatility of heterocystous cyanobacteria has also been summarized.