Cyanobacteria
are the most primitive group of photoautotrophic prokaryotic micro-flora,
probably appeared on the Earth during Precambrian era while there was no
ozone-shield and intense solar light with high incidence of harmful ultraviolet
(UV) radiation. Survival of life under extreme condition of UV radiation ishighly menacing. The high-energetic UV (280–400 nm) radiation has great
potential for cell damage either through direct effects on biologically relevant
key machinery such as DNA, proteins and lipids, or indirect effects via the
production of reactive oxygen species (ROS), leading to mutagenesis, and loss
of fundamental cellular physiology and metabolic functions.
However, in
the face of adverse effects of intense solar radiation, cyanobacteria developed
some efficient repair mechanisms along with various enzymatic/non-enzymaticdefense systems to counteract the harmful effects of UV radiation. Moreover,
owing to strong defense systems, cyanobacteria are so far surviving and
thriving well as dominant primary producers over a wide range of aquatic and
terrestrial ecosystems including the extreme habitats such as deserts, hot
springs, acidic, saline, and extremely cold polar region
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