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morphology, photosynthetic pigments and oxygenic photosynthesis with photosystems (PS II and PS I) similar to the algae. Later on, Herdman et al. [1] reported that the genome size of cyanobacteria (1.6 × 109 to 8.6 × 109 Da) was similar to bacteria (1.0 to 3.6 × 109 Da) and it was

Cyanobacteria are microscopic in size but their colonies or mats are quite conspicuous. The habitats of cyanobacteria are quite diversified in terms of their unique adaptability to an array of climatic conditions ranging from glaciers, sea, and lake to deserts. They are one of the harbingers of the biological organism that evolved on earth perhaps after the first bacteria, billions of years ago long prior to mankind. They are dynamic organisms inhabiting the most extreme habitats on the planet and can be readily relocated to new avenues via air. The morphological dynamics include unicellular, filamentous and colonies. The cells of cyanobacteria are bigger in size compared to usual cells of bacteria. The nature of cell wall is peptidoglycan and is multi-layered with photosynthetic pigments in the outer part of protoplast. A covering of mucin is seen on the filament and no locomotion system has been reported, though some

They are photosynthetic in nature yet they are reported to inhabit marginally illuminated caves while on the other extreme end, they dwell well at salty marshes, exposed to high light intensity [3]. The photosynthetic machinery of cyanobacteria is armored with a myriad pigments- chlorophylls, carotenoids, and phycobiliproteins-phycoerythrin, phycocyanin and allophycocyanin [4, 5]. The pigment system enables the wide range of adaptations to the alterations in light intensities [6, 7]. An outstanding phenomenon called complementary chromatic adaptation is evident in cyanobacteria wherein they adapt to changes in the intensity of light due to the phycobiliprotein synthesis in response to the wavelength of light. The pigments also aid in protecting the cells from the detrimental effects of harmful radiations [5]. They inhabit virtually all major aquatic and terrestrial biome on the earth by virtue of their unique adaptability. The low water potential dwelling cyanobacteria resist the desiccations by adapting to the high salinity as seen in the ponds with hypersaline conditions [8]. The temperature range that permits the growth of cyanobacteria is quite large ranging from freezing to 40°C, though the optimum temperature lies in between 20 and 35°C, while the open ocean cyanobacteria are exposed to the temperature nearly 30°C [9]. The pH requirements of cyanobacteria generally range from neutral to alkaline, but they have also been reported to inhabit hot springs which are acidic in nature [10, 11]. The primary mode of nutrition in cyanobacteria is photosynthesis but in the hydrogen sulfide-rich environment, switching from oxygenic to anoxygenic photosynthesis is reported [12, 13] which is similar in nature to

Cyanobacteria are very significant prokaryotes for the environment and plant growth. Though they are free-living organisms few live in symbiotic association with other eukaryotes and perform profound new roles essential for the ecosystem. They are the natural nitrogen fixings icons, which is quite essential for the entire biological system. The capability of converting atmospheric nitrogen into organic ammonia, nitrite or nitrate is called biological nitrogen fixation, though possessed by few organisms and essential for the growth of the plants. The talent of some cyanobacteria to bring about nitrogen fixation allows them to inhabit low nitrogen concentration ambiance, which is an added advantage in terms of survival and adapt-

advocated that cyanobacteria are more related to bacteria.

forms exhibit oscillatory motion [2].

4 Cyanobacteria

the bacterial type photosynthesis.

ability in the environment.

Archana Tiwari

Address all correspondence to: panarchana@gmail.com

Amity Institute of Biotechnology, Amity University, Noida, Uttar Pradesh, India
