Cyanobacteria are also known as Blue Green Algae. They are Gram positive prokaryotes. They are photosynthetic and have pigments like chlorophyll a, carotenoids, along with phycobilins. They have autotrophic mode of nutrition. They have thrived in almost every environment like hot springs, salt marshes, moist soils etc. They are one of the earliest colonizers. They can be unicellular, filamentous or occur in colonies. The filament has mucin covering. There are no flagella for locomotion of bacteria. Their cells are larger than normal bacterial cells. Their cell wall is multi layered. It includes peptidoglycan and there are photosynthetic pigments in outer part of protoplast. Some of them lie freely in the cytoplasm. Mostly all the photosynthetic pigment are present except chlorophyll b. There are minute granules which are attached to the photosynthetic pigment and are referred as Phycobilisomes. It also contains photosynthetic pigments known as Phycobilins.
Phycobilins are further of three types’ phycocyanin, allophycocyanin, and Phycoerythrin. They are blue and red in color and their color is not static. It may keep on changing. In this type of bacteria gas vacuoles are found which have small microscopic units known as Gas Vesicles. Vacuoles basically regulate buoyancy. There is naked circular double stranded DNA which is in the centre of cytoplasm known as centroplasm. It is equivalent to single large chromosome. It is also known as Nucleoid. They also contain plasmid and cell inclusions.
Heterocyst is large sized thick wall which occurs in sideways position of Cyanobacteria. These thick walls are permeable to nitrogen and impermeable to gas oxygen. There is no photosynthesis but photophosphorylation does occur. It depends on adjacent cell for its survival.
Reproduction Of Cyanobacteria
Cyanobacteria depend upon asexual methods for its division. Binary fission and fragmentation are most common methods. No sexual methods as there are no formation of gamete and there is absence of meiosis. However, conjugation, transformation and transduction do occur. Spore formation is also vital process.
Cyanobacteria serve as food for human consumption like spirulina and also for aquatic animals. From Sambar Lake in Rajasthan one can get spirulina and anabaena for manure and fodder. Spirulina also provides protein rich food. These bacteria also fix nitrogen and has special cell known as heterocyst for it. They are now days regularly used in agriculture fields. They are mainly used to preserve nitrogen. They can also reclaim the used soil. They also give rise to antibiotics and spread foul smell from water bodies.
Other common types of Cyanobacteria
Spirulina are coil free organisms which are up to half mm in length. They are unicellular and can be cultured. They have dual mode of nutrition that is autotrophic and heterotrophic. Locomotors movements like rotation and bending have been shown by Trichomes. They are rich in protein, vitamins such as B 12, minerals and fatty acids. It is also used as a food additive and is taunted as greatest super food by WHO. It is also good supplement for animals and they should not form more than 1/10 of their content. They also have medical value that is they act against viral and cancer cells.
Oscillatoria is found in almost every aquatic habitat. It is single, filamentous, un branched and hooked. It shows oscillations. Fragmentation is the most common mode of reproduction.
Anabaena is nitrogen fixing bacteria that is free to live in aquatic habitats. They also occur as symbiotic in some species. Heterocyst plays an important role in nitrogen fixation. They may also release some toxic contents.
Nostoc form colonies and is known as fallen star or star jelly. Along with aquatic habitats they are also found in sub aerial places. Their trichome is S shaped and has beads, with vegetative cells along with heterocyst and dormant cells known as akinetes. They have the ability to fix nitrogen and reclaim soil. They also act as a food supplement in China. Fragmentation and hormogones are the main methods of reproduction.