Cyanobacteria, also known as blue algae, are single-celled and belong to the family of Prokaryotes. That means, they do not have a cell nucleus. Over 3.5 billion years ago they first appeared, and thus belong to one of the oldest forms of life. Today we know of approximately 2000 different kinds of Cyanobacteria. In botany they are grouped with the rest of the bacteria, under the class of plants without nuclei. Cyanobacteria connect themselves through the creation of hyphae. These are clearly recognizable under the microscope, can link the cells together in clumps. Due to these morphologic characteristics Cyanobacteria can be arranged into five sections, whereby Cyanobacteria of sections 1 and 2 do not produce threadlike filaments and bacteria of the sections of 3, 4 and 5 do. Those of the fifth class also create a biofilm and connect with each other that way as well.

Procreation takes place by means of vegetative cell division.
Their nourishing system is photoautotrophic. They use light as an energy source for photosynthesis. With photosynthesis carbon dioxide and water are converted to glucose, a type of sugar, and simple oxygen. The cell respiration of heterotrophic life forms functions in the exact opposite method.
Cyanobacteria love humidity and occur in the many different habitats. They are found world-wide from the Arctic to the deserts.

Among these habitats water and frequently wet places rank among their favorites, such as soil, rocks or tree bark. Sometimes on rock and tree bark they form a symbiotic relationship with lichens and mushrooms. Some kinds also prefer the roots of higher plants for their favorite habitat. There are also specialists, who adapted to life in the desert. Under favorable conditions Cyanobacteria in our lakes and ponds can increase like an explosion. This results in the well-known algae bloom which can result in the eutrophication of the lake or pond.

The Cyanobacteria are very unpopular with swimmers, because they spoil the experience by covering the surface of the water with slimy algae and smell rather strongly. In addition such algae blooms can lead to the complete silting of the body of water.

Nearly all Cyanobacteria produce strong toxins like Microcystin, which can kill fish. The poisons are dangerous not only for water inhabitants, but also for humans and sometimes plants. The hyphae develop two separate types of cells. Beside the photosynthetic cells they also create heterozysten. These are specialized cells, which are responsible for the absorption of elementary nitrogen (N₂) from the atmosphere. The ability to operate photosynthesis is missing in the Heterozysten however. Elementary nitrogen is reduced to ammonium (NH₄⁺). Nitrogen is important for plants as well as phosphor for their growth. In addition it is needed by protein synthesis into amino acids. This ability to bind nitrogen was the reason for our desire to closely examine these life forms.

Sources:
Lexikon der Baum und Straucharten, Schütt – Schuck – Stimm, Verlag: Nikol
Das große Buch des Allgemeinwissens Natur, Verlag: Gondrom
Drewings Biohefte
Powerpoint-Präsentation von Herrn Kurmayer
http://lexikon.meyers.de/wissen/Cyanobakterien+(Sachartikel)
http://de.wikipedia.org/wiki/Cyanobakterien
http://www.uni-protokolle.de/nachrichten/id/49595/
http://www.wipo.int/pctdb/en/wo.jsp?wo=2005074622&IA=US2005003314&DISPLAY=DESC
http://microbewiki.kenyon.edu/index.php/Nostoc
L. Geitler 1925. Die Süsswasserflora Deutschlands, Österreichs und der Schweiz. Heft 12: Cyanophyceae. Jena, Verlag von Gustav Fischer.