Cyanobacteria Synthesize their own UV-Sunscreens for Photoprotection

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

Preventing Overproduction of Reactive Oxygen Species is a Universal Survival Strategy: Physiological Uncoupling

The highly exergonic reduction of O2 by aerobic organisms yields large amounts of energy. However, the production of toxic partiallyreduced side-reaction products, collectively termed Reactive Oxygen Species(ROS) is a major problem.While ROS detoxification is thoroughly investigated, control of ROS production needs to be analyzed in depth. Uncoupling O2 consumption from ATP synthesis increases electron flow and decreases ROS production. Physiological uncoupling, however, must be tightly controlled to avoid energy depletion and death.

Uncoupling mechanisms include proton sinks, such as mitochondrial permeability transition pores and uncoupling proteins. Protonsinks have not been described in prokaryotes. Instead, prokaryotes, as well as unicellular eukaryotes, arthropods and plants may contain branched respiratory chains.