Cyanobacteria

The Cyanobacteria are a uniformly phototrophic phylum but differ fundamentally from apparently same photosynthetic Proteobacteria like as Rhodococcus. They can be sub- divided into five groups according to their cellular morphology that are filamentous or unicellular, nonbranching, branching, etc. and in this case the morphology has significance in their phylogeny. All produce complex membranes in that photosynthesis takes place. The cells are green-blue in color due to the presence of chlorophyll a and phycobilins on the cell membrane giving the phylum its present name. The filamentous varieties can show cellular structural differentiation with a few cells forming gas vesicles or heterocysts. The genera Synechococcus, Anabaena and Prochloron are the best studied.