Firstly cyanobacteria are kept in as myxophyceae of class algae (blue-green algae). Later some phycologists kept it into Cyanophyceae, while others kept it into Schizophyceae also. On the basis of the electron microscope and biochemistry Echlin and Moris that cyanobacteria show great affinity with blue-green algae.
Under the rules of the International Code of Nomenclature of bacteria (1978), blue-green algae have been proposed to be named Cyanobacteria by some bacteriologists.
According to Kunisawa, Mandel, Cohn, and Bezire, the organisms of cyanobacteria are not algae and they form a major group of bacteria. The group of blue-green algae, which are chlorophyllous and photosynthetic is called cyanobacteria.
Greek word “cyano” = blue and “bact” = rod
The absence of a definite nucleus with typical chromosomes, and the distribution of the pigments in a primitive chromatophore structure, shows their close resemblance with bacteria.
Cyanobacteria are the oxygenic photosynthetic bacteria growing on the surface of freshly exposed rocks, results in the deposition of organic matter due to the accumulation of their cells.
Salient features of Cyanobacteria:
Their major characteristics features are-
- Its members are blue in color due to the presence of phycocyanin pigment like; chlorophyll-a, carotene, and phycoerythrin also occur.
- Pigments are distributed in the cytoplasm instead of chromatophores.
- The true nucleus is absent.
- The nuclear membrane and nucleolus are absent.
- Cell divisions occur through protoplasm division and septum formation.
- Reserve food glycogen is similar to cyanophycean starch.
- Reproductive units are non-flagellate, hence non-motile.
- Sexual reproduction is completely absent.
- The mucilaginous or gelatinous sheath is present on the thallus.
- Pyrenoids are absent.
- These are prokaryotes, which lakes plastids, vacuoles, mitochondria, Golgi body, and endoplasmic reticulum.
- The cell wall is without cellulose.
- The cell wall contains 8 amino acids with peptides and aloha diaminopimelic acid and glucosamine.
Similarities between Cyanobacteria(blue-green algae) and Bacteria:
- presence of a prokaryotic nucleus.
- absence of well-organized plastids.
- presence of sheaths.
- ability to fix atmospheric nitrogen.
Differences of Cyanobacteria with Bacteria:
- Chlorophyll-a is absent in bacteria
- Magnesium porphyrin compound is present in photosynthetic bacteria which is similar to chlorophyll-a.
- Heterocyst is absent in bacteria.
- Photosynthetic bacteria produced Oxygen.
The few common genera of blue-green algae are Aulosira, Nostoc, Stigonema, Spirulina, Syctonema, Gloeocapsa, Chrococcus, etc.