Life of wetland cyanobacteria under enhancing solar UV-B radiation

The continuing depletion of stratospheric ozone layer mainly due to anthropogenically released pollutants such as chlorofluorocarbons (CFCs) has resulted in an increase in solar ultraviolet-B (UV-B; 280 - 315 nm) radiation reaching to the Earth's surface. UV-B is a small (less than 1% of total energy) but highly active component of solar radiation that can penetrate deep into biologically significant depths in lakes, ponds, rivers and oceans. Photosynthetic prokaryotes such as cyanobacteria are dependent on solar energy and thereby always sense and face the stress of UV-B radiation. UV-B can cause wide ranging effects including mutagenesis, destruction of proteins/enzymes, inhibition of a number of vital metabolic processes and formation of thymine dimers in DNA leading to death of microbes. The degree of damaging effects brought about by UV-B varies in different species suggesting the existence of certain protective mechanisms operative in cyanobacteria. A number of species counteract the damaging effects of UV-B by synthesizing UV protective compounds such as mycosporine-like amino acids (MAAs) and the sheath pigment, scytonemin. These compounds are known to act as natural sunscreens and their synthesis is induced by UV-B radiation. In this article an attempt has been made to highlight some of the notable effects or UV-B radiation on wetland cyanobacteria and the role of photoprotective mechanisms in mitigating the damage.