Ultraviolet radiation and cyanobacteria

Abstract

Cyanobacteria are the dominant photosynthetic prokaryotes from an ecological, economical, or evolutionary perspective, and depend on solar energy to conduct their normal life processes. However, the marked increase in solar ultraviolet radiation (UVR) caused by the continuous depletion of the stratospheric ozone shield has fueled serious concerns about the ecological consequences for all living organisms, including cyanobacteria. UV-B radiation can damage cellular DNA and several physiological and biochemical processes in cyanobacterial cells, either directly, through its interaction with certain biomolecules that absorb in the UV range, or indirectly, with the oxidative stress exerted by reactive oxygen species. However, cyanobacteria have a long history of survival on Earth, and they predate the existence of the present ozone shield. To withstand the detrimental effects of solar UVR, these prokaryotes have evolved several lines of defense and various tolerance mechanisms, including avoidance, antioxidant production, DNA repair, protein resynthesis, programmed cell death, and the synthesis of UV-absorbing/screening compounds, such as mycosporine-like amino acids (MAAs) and scytonemin. This study critically reviews the current information on the effects of UVR on several physiological and biochemical processes of cyanobacteria and the various tolerance mechanisms they have developed. Genomic insights into the biosynthesis of MAAs and scytonemin and recent advances in our understanding of the roles of exopolysaccharides and heat shock proteins in photoprotection are also discussed.

Cyanobacterial Sunscreen Scytonemin: Role in Photoprotection and Biomedical Research

“…1 Effects of solar UV radiation on diverse photosynthetic life including cyanobacteria, and subsequent adoption of different defense mechanisms to counteract the harmful effects of short wavelength solar energy (for details see ref. [5]). [Image from R. P. Rastogi] …”

“…1) [5][6][7]. Moreover, a number of biochemical defense mechanisms such as genome repair and synthesis of certain antioxidant and photoprotective compounds have been developed by several taxonomic groups including cyanobacteria to overcome the damaging effects of short wavelength UV radiation [5,[8][9][10][11][12].…”

“…1) [5][6][7]. Moreover, a number of biochemical defense mechanisms such as genome repair and synthesis of certain antioxidant and photoprotective compounds have been developed by several taxonomic groups including cyanobacteria to overcome the damaging effects of short wavelength UV radiation [5,[8][9][10][11][12]. Biosynthesis of some UV-absorbing compounds such as mycosporine-like amino acids (MAAs) and scytonemin which are considered as the potent sunscreening biomolecules due to their putative role in UV photoprotection [13][14][15][16][17][18][19] is observed.…”

Pigment mutants of the green microalga Chlamydomonas reinhardtii: Morphological properties and photosynthetic performance

“…The pigment content is an integral index that determines not only the development and activity of the photosynthetic system but also the time course of many enzymatic reactions; i.e., it characterizes the productivity, viability, and resistance of plant organisms [14]. Irradiation with UV-B disrupts the functioning of plant pigment systems, disturbs the content and composition of pigments.…”

Inhibitory effects ofAphanizomenon flos-aquaeconstituents on human UDP-glucose dehydrogenase activity

“…The strong antioxidant activity of the protein originates from covalently attached linear tetrapyrrole prosthetic groups known as phycocyanobilins (PCB) 22 . MAAs are watersoluble low molecular weight compounds, which have UVabsorbing properties and antioxidant activities 25,26 . In addition, we have recently demonstrated that AFA MAAs show a competitive type of inhibition towards monoamine oxidase B activity 20 .…”