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Mechanisms of Photoprotection in Cyanobacteria
(Elsevier, 2018) Jainendra Pathak; Haseen Ahmed; Prashant R. Singh; Shailendra P. Singh; Donat-P. Häder; Rajeshwar P. Sinha
Cyanobacteria represent a unique group of prokaryotes that are able to perform oxygenic photosynthesis and constitute crucial microflora with respect to total biomass and productivity in terrestrial and aquatic ecosystems. They are natural biofertilizers and also serve as potent source of natural products of industrial and medicinal values. Harvesting of light for photosynthesis exposes cyanobacteria to unpredictable changes in light intensity and harmful doses of solar ultraviolet radiation (UVR). High light intensity induces photooxidative damage of the reaction centers due to the generation of reactive oxygen species and hence, is lethal for cyanobacteria. UVR adversely affects several biological processes, such as growth, development, orientation and motility, photosynthesis, pigmentation, CO2 assimilation, enzyme activity, and N2 fixation. DNA shows absorption in the UV range, hence, is one of the prime targets of UVR. Inclusive survival of cyanobacteria in diverse ecological niches and adaptive diversification have compelled them to evolve an array of survival strategies to compete and sustain successfully in different environments with high light intensity together with UV fluxes on the Earth. Photoprotective mechanisms such as avoidance, nonphotochemical quenching to dissipate excess excited-state energy as heat, synthesis of photoactive proteins such as orange carotenoid protein, fluorescence recovery protein, early shock proteins, late acclimation proteins, antioxidative enzymes, sunscreens such as scytonemin and mycosporine-like amino acids, repair, and programmed cell death are adapted by cyanobacteria to counteract the damage caused by high light conditions and UVR. This chapter provides an in-depth account of important mechanisms involved in photoprotection in cyanobacteria. © 2019 Elsevier Inc. All rights reserved.
Photoprotective compounds from marine organisms
(Springer Verlag, 2010) Rajesh P. Rastogi; Richa; Rajeshwar P. Sinha; Shailendra P. Singh; Donat-P. Häder
The substantial loss in the stratospheric ozone layer and consequent increase in solar ultraviolet radiation on the earth's surface have augmented the interest in searching for natural photoprotective compounds in organisms of marine as well as freshwater ecosystems. A number of photoprotective compounds such as mycosporine- like amino acids (MAAs), scytonemin, carotenoids and several other UV-absorbing substances of unknown chemical structure have been identified from different organisms. MAAs form the most common class of UVabsorbing compounds known to occur widely in various marine organisms; however, several compounds having UV-screening properties still need to be identified. The synthesis of scytonemin, a predominant UV-A- photoprotectivepigment, is exclusively reported in cyanobacteria. Carotenoids are important components of the photosynthetic apparatus that serve both light-harvesting and photoprotective functions, either by direct quenching of the singlet oxygen or other toxic reactive oxygen species or by dissipating the excess energy in the photosynthetic apparatus. The production of photoprotective compounds is affected by several environmental factors such as different wavelengths of UVR, desiccation, nutrients, salt concentration, light as well as dark period, and still there is controversy about the biosynthesis of various photoprotective compounds. Recent studies have focused on marine organisms as a source of natural bioactive molecules having a photoprotective role, their biosynthesis and commercial application. However, there is a need for extensive work to explore the photoprotective role of various UVabsorbing compounds from marine habitats so that a range of biotechnological and pharmaceutical applications can be found. © Society for Industrial Microbiology 2010.
Physiological responses of the cyanobacterium Synechocystis sp. PCC 6803 under rhythmic light variations
(Springer Nature, 2023) Prashant R. Singh; Jainendra Pathak; Rajneesh; Haseen Ahmed; Donat-P. Häder; Rajeshwar P. Sinha
Cyanobacteria are challenged by daily fluctuations of light intensities and photoperiod in their natural habitats, which affect the physiology and fitness of cyanobacteria. Circadian rhythms (CRs), an important endogenous process found in all organisms including cyanobacteria, control their physiological activities and helps in coping with 24-h light/dark (LD) cycle. In cyanobacteria, physiological responses under rhythmic ultraviolet radiation (UVR) are poorly studied. Therefore, we studied the changes in photosynthetic pigments, and physiological parameters of Synechocystis sp. PCC 6803 under UVR and photosynthetically active radiation (PAR) of light/dark (LD) oscillations having the combinations of 0, 4:20, 8:16, 12:12, 16:8, 20:4, and 24:24 h. The LD 16:8 enhanced the growth, pigments, proteins, photosynthetic efficiency, and physiology of Synechocystis sp. PCC6803. Continuous light (LL 24) of UVR and PAR exerted negative impact on the photosynthetic pigments, and chlorophyll fluorescence. Significant increase in reactive oxygen species (ROS) resulted in loss of plasma membrane integrity followed by decreased viability of cells. The dark phase played a significant role in Synechocystis to withstand the LL 24 under PAR and UVR. This study offers detailed understanding of the physiological responses of the cyanobacterium to changing light environment. © 2023, The Author(s), under exclusive licence to European Photochemistry Association, European Society for Photobiology.
Photoheterotrophic growth unprecedentedly increases the biosynthesis of mycosporine-like amino acid shinorine in the cyanobacterium Anabaena sp., isolated from hot springs of Rajgir (India)
(2014) Shailendra P. Singh; Sun-yong Ha; Rajeshwar P. Sinha; Donat-P. Häder
Cyanobacteria are known to biosynthesize mycosporine-like amino acids (MAAs) as photoprotective compounds against ultraviolet radiation. Anabaena sp., isolated from the hot springs of Rajgir, India, produces a single MAA shinorine (retention time = 2.2 min and absorption maximum at 334 nm) as purified by high-performance liquid chromatography. The MAA biosynthesis was under constitutive control in this cyanobacterium; however, PAR + UV-A + UV-B radiation was found to have highest impact on MAA synthesis. MAA biosynthesis is dependent on photosynthesis for the carbon source since the inhibitory effect of DCMU on MAA synthesis was overcome by externally added fructose. Our results suggest that there is no direct involvement of photosystem II dependent linear electron transport in MAA biosynthesis. However, utilization of energy derived from photosystem I dependent cyclic electron transport in MAA biosynthesis cannot be ruled out. This study also reveals that photoheterotrophic growth can support highest MAA biosynthesis under laboratory conditions in comparison with photoautotrophic and photomixotrophic growth. Thus, photoheterotrophic growth condition can be used for the large-scale production of pharmaceutically important MAAs from cyanobacteria for an industrial application. © 2013 Franciszek Górski Institute of Plant Physiology, Polish Academy of Sciences, Kraków.
Cyanobacteria and ultraviolet radiation (UVR) stress: Mitigation strategies
(2010) Shailendra P. Singh; Donat-P. Häder; Rajeshwar P. Sinha
Cyanobacteria are primitive photosynthetic oxygen-evolving prokaryotes that appeared on the Earth when there was no ozone layer to protect them from damaging ultraviolet radiation (UVR). UVR has both direct and indirect effects on the cyanobacteria due to absorption by biomolecules and UVR-induced oxidative stress, respectively. However, these organisms have developed several lines of mitigation strategies/defense mechanisms such as avoidance, scavenging, screening, repair and programmed cell death to counteract the damaging effects of UVR. This review presents an update on the effects of UVR on cyanobacteria and the defense mechanisms employed by these prokaryotes to withstand UVR stress. In addition, recent developments in the field of molecular biology of UV-absorbing compounds such as mycosporine-like amino acids and scytonemin, are also added and the possible role of programmed cell death, signal perception as well their transduction under UVR stress is being discussed. © 2009 Elsevier Ireland Ltd. All rights reserved.
Ultraviolet-B-induced DNA damage and photorepair in the cyanobacterium Anabaena variabilis PCC 7937
(2011) Rajesh P. Rastogi; Shailendra P. Singh; Donat-P. Häder; Rajeshwar P. Sinha
The impact of simulated solar radiation on DNA and the mitigation of DNA-damaging effects by photoreactivation was studied in a cyanobacterium Anabaena variabilis PCC 7937. Cultures were irradiated under 295, 320 and 395. nm cut-off filters as well as seven other filters such as WG 280, WG 295, WG 305, WG 320, WG 335, WG 345 and GG 400. Growth of the test organism was found to be affected mostly under UV-B radiation as compared to PAR and PAR. +. UV-A radiations. Amplification of 16s rDNA and RAPD profile was significantly affected following exposure of genomic DNA to UV-B radiation. The formation of T<>T CPDs was recorded only in the cultures irradiated with UV-B radiation (i.e., under 295. nm as well as under WG 280, WG 295 and WG 305. nm cut-off filters), but maximum yield was found under 280. nm cut-off filter. Furthermore, the considerable induction of thymine dimers was observed with increasing UV-irradiation times. Fluorometric analysis of DNA unwinding (FADU) assay for UV-induced DNA strand breaks exhibited the maximum loss in the percentage of dsDNA under UV-B radiation followed by UV-A and PAR in comparison to the light control samples. We observed that T<>T CPD repair is light-dependent, since these lesions were more efficiently removed upon exposure to visible light than in the darkness. Blue radiation was found to be the most effective in photoreactivation than any other wavebands of light. Furthermore, the rate of photoreactivation was measured under varying temperatures (10, 20 and 30 °C); the repair rate was found to be the maximum at 20 °C under white fluorescent light. Our results indicate that photoreactivation play an important role in survival of the organism under natural conditions in spite of being exposed to the UV-B component present in the solar drops. © 2011 Elsevier B.V.
Genetic regulation of scytonemin and mycosporine-like amino acids (MAAs) biosynthesis in cyanobacteria
(Elsevier B.V., 2019) Jainendra Pathak; Haseen Ahmed; Rajneesh; Shailendra P. Singh; Donat-P. Häder; Rajeshwar P. Sinha
Scytonemin and mycosporine-like amino acids (MAAs) are important novel secondary metabolites synthesized by cyanobacteria to protect themselves from lethal ultraviolet (UV) radiation. Scytonemin, the extracellular polysaccharide sheath pigment is found in several cyanobacterial species and is a lipid-soluble dimeric pigment consisting of phenolic and indolic subunits linked through an olefinic carbon atom. Structure of MAAs consists of aminocyclohexenone or an aminocyclohexinimine chrompohore conjugated with the nitrogen substituent of an amino acid or its amino alcohol. MAAs are small, colorless water soluble compounds. These UV screening compounds are highly photostable photoprotectant and also serve as potent antioxidants. Multiple environmental signals influence scytonemin and MAAs synthesis and regulation of induction of these UV screening compounds is a part of complex stress response pathway. Hence, proper understanding of genetic regulation and biosynthesis of these microbial sunscreens would not only provide scientific insight in a major class of secondary metabolites but will also help in commercial production of these new age ecofriendly sunscreens. © 2019
UV-protectants in cyanobacteria
(2008) Rajeshwar P. Sinha; Donat-P. Häder
Cyanobacteria are the largest group of Gram-negative photosynthetic prokaryotes on earth and have a cosmopolitan distribution. As cyanobacteria are believed to have originated in the Precambrian era at a time when the ozone shield was absent, they presumably faced high fluxes of UV radiation, which must have acted as an evolutionary pressure leading to the selection for efficient UV radiation protecting mechanisms. Tolerance of cyanobacteria to intense sunlight as well as UV radiation might have contributed to their success during early stages of colonization. The synthesis of UV-absorbing/screening compounds is an important mechanism to prevent UV-induced photodamage. In cyanobacteria photoprotectants such as mycosporine-like amino acids (MAAs) and scytonemin strongly absorb in the UV-A and/or UV-B region of the spectrum, and thus play an important role in allowing these organisms to grow and survive in habitats exposed to strong irradiation. © 2007 Elsevier Ireland Ltd. All rights reserved.
UV-B-induced synthesis of mycosporine-like amino acids in three strains of Nodularia (cyanobacteria)
(Elsevier, 2003) Rajeshwar P. Sinha; Navin K. Ambasht; Jiweshwar P. Sinha; Manfred Klisch; Donat-P. Häder
Three filamentous and heterocystous cyanobacterial strains of Nodularia, Nodularia baltica, Nodularia harveyana and Nodularia spumigena, have been tested for the presence and induction of ultraviolet-absorbing/screening mycosporine-like amino acids (MAAs) by simulated solar radiation in combination with 395 (receiving photosynthetically active radiation (PAR) only), 320 (receiving PAR + UV-A) and 295 (receiving PAR + UV-A + UV-B) nm cut-off filters. Absorption spectroscopic analyses of the methanolic extracts of samples revealed a typical MAA peak at 334 nm in all three cyanobacteria. Specific contents of MAAs had a pronounced induction in the samples covered with 295 nm cut-off filters after 72 h of irradiation. In comparison, there was little induction of MAAs in the samples covered by 395 and 320 nm cut-off filters. High performance liquid chromatographic (HPLC) studies revealed the presence of two types of MAAs in all three cyanobacteria, which were identified as shinorine and porphyra-334, both absorbing maximally at 334 nm. The occurrence of porphyra-334 is rare in cyanobacteria. Specific content of both shinorine and porphyra-334 were induced remarkably only in the samples covered with 295 nm cut-off filters. The results indicate that in comparison to UV-A and PAR, UV-B is more effective in eliciting MAAs induction in the studied cyanobacteria. © 2003 Elsevier B.V. All rights reserved.
An improved method for genomic DNA extraction from cyanobacteria
(Kluwer Academic Publishers, 2011) Shailendra P. Singh; Rajesh P. Rastogi; Donat-P. Häder; Rajeshwar P. Sinha
We present an improved method for genomic DNA extraction from cyanobacteria by updating the earlier method from our group (Sinha et al. 2001) that does not require lysozyme treatment or sonication to lyse the cells. This method use lysis buffer to lyse the cells and also skips the initial treatments to remove the exopolysaccharides or to break the clumps. To test the efficacy of the method DNA was extracted from the freshwater cyanobacteria Anabaena variabilis PCC 7937, Anabaena sp. PCC 7120, Synechocystis sp. PCC 6803, Synechococcus sp. PCC 6301 and Rivularia sp. HKAR-4 (Accession number: FJ939128). The spectrophotometric and gel electrophoresis analysis revealed high yield and high quality of genomic DNA extracted by this method. Furthermore, the RAPD resulted in the amplification of unidentified genomic regions of various lengths; however, rDNA amplification gave only one band of 1. 5 kb in all studied cyanobacteria. Thymine dimer detection study revealed that thymine dimers are induced only by UV-B radiation in A. variabilis PCC 7937 and there is no effect of PAR and UV-A on its genome. Collectively, all these findings put forward the applicability of this method in different studies and purposes. © 2010 Springer Science+Business Media B.V.

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