About blue-green bacteria - Cyanobacteria
Blue-green algae or blue-green bacteria, mainly live in freshwater, and mostly in water rich in nutrients. All the pictures of blue-green algae in this program are taken from fresh-water.
Yet the blue-green algae play a role in the seawater. The blue green specimen Trichodesmium erythraeum, which is characterized by a red pigment, sometimes occurs in enormous quantities in the Red Sea, and is in fact responsible for the name of this area of sea.
The blue-green bacteria are often considered to have been the organisms responsible for the early accumulation of oxygen in the earth's atmosphere.
The pictures shows examples of some normal species. From the left: Anabaena,
Microcystis, Merismopedia og Chroococcus
The cell structure of blue-green algae is bacterial in nature and therefore the correct group name is blue-green bacteria. They belong to the oldest group of organisms we know.
All blue-green bacteria are unicellular, without any cilia or flagella. They live single or the cells are combined in colonial and filamentous forms without any functional connection between the cells. The colonies are hold together by mucilage which can contain several thousands very small cells, or they form tabular colonies one cell thick. The number of cells in a colony can range from a few to several thousands.
The group is widespread in different systems as freshwater, seawater, in earth and even in extreme places like ice, deserts and warm springs. Some blue-green bacteria, like Anabaena species, have gas vesicles in their cells and so they can live in the surface of the water. In a water bloom they can be present in enormous numbers. The cells only reproduce by dividing in two.
The water bloom is applied to surface accumulation of gas-vacuolated blue green bacteria. The appearance of water bloom is considered to be a sign of undesirable changes in water quality. Some of the blue-green-bacteria contain toxic substances.