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Blue and red light significantly aid in the recovery of damaged cells of the cyanobacterium Synechocystis sp. PCC 6803 exposed to ultraviolet radiation
(Springer Nature, 2025) Prashant R. Singh; Ashish P. Singh; Amit Gupta; Shailendra P. Singh; Rajeshwar Prasad Sinha
Cyanobacteria are the most promising models for CO2 sequestration, production of chemicals, and renewal energy. Being photosynthetic organisms, they are continuously exposed to different intensities and wavelengths of light, including ultraviolet radiation (UVR). In the present investigation, we studied photosynthetically active radiation (PAR + UV−A + UV−B (PAB) effects on the cyanobacterium Synechocystis sp. PCC 6803 and its recovery under different wavelengths of light, such as PAR, blue light (BL), green light (GL), and red light (RL). The Chl a and total carotenoid content recovered maximally under BL and RL, whereas phycocyanin (PC) under BL. Maximum recovery in the photosynthetic performance was observed under GL and RL, whereas the least recovery was under BL. After 48 h of PAB irradiation, minimum ROS was found under dark conditions. The maximum number of non-viable cells was found in 24 h PAB, and in the recovery phase, it was found in BL and RL. Thus, it was evident that PAB negatively affects the growth, development, and overall fitness of Synechocystis sp. PCC 6803. The different wavelengths of light play a significant role in the recovery of the cyanobacterium Synechocystis sp. PCC 6803. © The Author(s), under exclusive licence to the European Photochemistry Association, European Society for Photobiology 2025.
RcaE-dependent regulation of carboxysome structural proteins has a central role in environmental determination of carboxysome morphology and abundance in Fremyella diplosiphon
(American Society for Microbiology, 2018) Brandon A. Rohnke; Shailendra P. Singh; Bagmi Pattanaik; Beronda L. Montgomery
Carboxysomes are central to the carbon dioxide-concentrating mechanism (CCM) and carbon fixation in cyanobacteria. Although the structure is well understood, roles of environmental cues in the synthesis, positioning, and functional tuning of carboxysomes have not been systematically studied. Fremyella diplosiphon is a model cyanobacterium for assessing impacts of environmental light cues on photosynthetic pigmentation and tuning of photosynthetic efficiency during complementary chromatic acclimation (CCA), which is controlled by the photoreceptor RcaE. Given the central role of carboxysomes in photosynthesis, we investigated roles of light-dependent RcaE signaling in carboxysome structure and function. A ΔrcaE mutant exhibits altered carboxysome size and number, ccm gene expression, and carboxysome protein accumulation relative to the wild-type (WT) strain. Several Ccm proteins, including carboxysome shell proteins and core-nucleating factors, overaccumulate in ΔrcaE cells relative to WT cells. Additionally, levels of carboxysome cargo RuBisCO in the ΔrcaE mutant are lower than or unchanged from those in the WT strain. This shift in the ratios of carboxysome shell and nucleating components to the carboxysome cargo appears to drive carboxysome morphology and abundance dynamics. Carboxysomes are also occasionally mislocalized spatially to the periphery of spherical mutants within thylakoid membranes, suggesting that carboxysome positioning is impacted by cell shape. The RcaE photoreceptor links perception of external light cues to regulating carboxysome structure and function and, thus, to the cellular capacity for carbon fixation. © 2018 Rohnke et al.
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.
Flow Cytometry-based Measurement of Reactive Oxygen Species in Cyanobacteria
(Bio-protocol LLC, 2022) Soumila Mondal; Shailendra P. Singh
Cyanobacteria are Gram-negative oxygen-producing photosynthetic bacteria that are useful in the pharmaceutical and biofuel industries. Monitoring of oxidative stress under fluctuating environmental conditions is important for determining the fitness, survival, and growth of cyanobacteria in the laboratory as well as in large scale cultivation systems. Here, we provide a protocol developed using unicellular Synechococcus elongatus PCC 7942 and filamentous Fremyella diplosiphon BK14 cyanobacteria for high-throughput oxidative stress measurement by 2′,7′-dichlorodihydrofluorescein-diacetate (DCFH-DA) and flow cytometry (FCM). We also provide details for the optimization of cell number, dye concentration, and FCM parameters for each organism before it can be utilized to quantify reactive oxygen species (ROS). FCM-based method can be used to measure ROS in a large population of cyanobacterial cells in a high-throughput manner. © 2022 The Authors; exclusive licensee Bio-protocol LLC.
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.
Photoprotective and biotechnological potentials of cyanobacterial sheath pigment, scytonemin
(2010) Shailendra P. Singh; Sunita Kumari; Rajesh P. Rastogi; Kanchan L. Singh; Richa P. Sinha; Rajeshwar P. Sinha
Cyanobacteria are the main component of microbial populations fixing atmospheric nitrogen in aquatic as well as terrestrial ecosystems, especially in wetland rice-fields, where they significantly contribute to fertility as natural biofertilizers. Cyanobacteria require solar radiation as their primary source of energy to carry out both photosynthesis and nitrogen fixation. The stratospheric ozone depletion which has resulted in an increase in ultraviolet-B (UV-B; 280 - 315 nm) radiation on earth's surface has been reported to inhibit a number of photochemical and photobiological processes in cyanobacteria. However, certain cyanobacteria have evolved mechanisms such as synthesis of photoprotective compound scytonemin and their derivatives to counteract the damaging effects of UV-B. In addition this compound has anti-inflammatory and anti-proliferative potentials. This review deals with the role of scytonemin as photoprotective compound and its pharmacological as well as biotechnological potentials. © 2010 Academic Journals.
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.
Computational studies on photolyase (Phr) proteins of cyanobacteria
(Canadian Science Publishing, 2022) Rajneesh; Soumila Mondal; Jainendra Pathak; Prashant R. Singh; Shailendra P. Singh; Rajeshwar P. Sinha
Photolyases (Phrs) are enzymes that utilize the blue/ultraviolet (UV-A) region of light for repairing UV-induced cyclopyramidine dimers. We studied Phr groups by bioinformatic analyses as well as active-site and structural modeling. Analysis of 238 amino acid sequences from 85 completely sequenced cyanobacterial genomes revealed five classes of Phrs, CPD Gr I, 6-4 Phrs/cryptochrome, Cry-DASH, Fe-S bacteria Phrs, and a group with fewer amino acids (276–385) in length. The distribution of Phr groups in cyanobacteria belonging to the order Synechococcales was found to be influenced by the habitats of the organisms. Class V Phrs are exclusively present in cyanobacteria. Unique motifs and binding sites were reported in groups II and III. The Fe-S protein binding site was only present in group V and the active site residues and putative CPD/6-4PP binding residues are charged amino acids present on the surface of the proteins. The majority of hydrophilic amino acid residues were present on the surface of the Phrs. Sequence analysis confirmed the diverse nature of Phrs, although sequence diversity did not affect the overall three-dimensional structure. Protein–ligand interaction analysis identified novel CPD/6-4PP binding sites on Phrs. This structural information of Phrs can be used for the preparation of efficient Phr-based formulations. © 2021 The Author(s).

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