Cyanobacteria, once popularly known as blue-green algae, are prokaryotes which exhibit very unusual characteristics unlike other prokaryotes. With very simple undifferentiated internal cellular organization without any membrane-bound organelles, they carry out three important physiological functions viz., oxygenic photosynthesis using chl a and other accessory pigments unlike photosynthetic bacteria which use bacteriochlorophyll, N2 fixation by oxygen-sensitive nitrogenase as free-living N fixers and in symbiotic association and inorganic N reduction pathway, all three features which are not found together in any other prokaryote or eukaryote. a small number of strains can also use hydrogen sulfide (H2S) and convert it to elemental sulfur. This review is restricted only to special features of Cyanobacteria
Heterocysts, nitrogenase, phycobilins
