a phylum of oxygenic photosynthetic bacteria comprised of unicellular to multicellular bacteria possessing chlorophyll a and carrying out oxygenic photosynthesis. cyanobacteria are the only known organisms capable of fixing both carbon dioxide (in the presence of light) and nitrogen. cell morphology can include nitrogen-fixing heterocysts and/or resting cells called akinetes. formerly called blue-green algae, cyanobacteria were traditionally treated as algae.
