Definitions for "cyanobacterium"
any of a group of photosynthetic autotrophic prokaryotic microorganisms possessing characteristics of both bacteria and plants. When classed as bacteria, they are assigned to the Cyanobacteria; when classed as plants, they are assigned to the Cyanophyta. They were earlier named blue-green algae, a term less used now in technical discussions. Since the chlorophyll within the cyanobacteria is diffused throughout the cell, rather than being contained in chloroplasts, they are no longer thought of as true plants.
a prokaryotic photosynthesizing life-form
photosynthetic bacterium of the class Coccogoneae or Hormogoneae, generally blue-green in color and in some species capable of nitrogen fixation. Cyanobacteria were once thought to be algae. Also called blue-green alga. the protoplasm of a cell excluding the nucleus.