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UV-induced physiological changes and biochemical characterization of mycosporine-like amino acid in a rice-field cyanobacterium Fischerella sp. strain HKAR-13
(Elsevier B.V., 2022) Vidya Singh; Jainendra Pathak; Abha Pandey; Haseen Ahmed; Rajneesh; Deepak Kumar; Rajeshwar P. Sinha
Mycosporine-like amino acids (MAAs) are valuable secondary metabolite with notable photoprotective potential. The present study investigateS the imрасts of рhоtоsynthetiс асtive rаdiаtiоn (РАR) and ultraviolet radiation (UVR) on various physiological processes in the cyanobacterium Fischerella sp. strain HKAR-13. Cell viability was reduced by 36 and 65% after 72h of exроsure to РАR+UV-А (PA) and РАR+UV-А+UV-B (PAB) radiations respectively. Significant decline in Chl a content was observed during PA and PAB exposure after 36h. Carotenoid content increased significantly after 48h of exposure, thereafter began to decline. Cultures exposed to PAB showed maximum detrimental effect on protein synthesis. In PAB and PA, the levels of intracellular reactive oxygen species (ROS) increased significantly. Fluorescence microscopic images of cyanobacteria revealed generation of ROS in UVR as indicated by increase in green fluorescence. Besides, Fischerella sp. strain HKAR-13 was also tested for the рresenсe of MААs and their induction under UVR. UV-Vis spectrophotometry and high-рerfоrmаnсe liquid сhrоmаtоgrарhy аnаlyses revealed the рresenсe of a MAA having absorption maxima λmax 334 nm and retention time of 1.5 min. Maximum induction of MAA was found in samples exposed to PAB followed by PA. Based on electrospray ionization-mass sрeсtrоsсорy (m/z: 333+1), fourier transform infrared and nuclear magnetic resоnаnсe sрeсtrоsсорy, the MAA was identified as shinorine. Shinorine was found to be highly stable under some abiotic stress factors such as UV-B, temperature and H2O2. It also showed efficient antioxidant activity in a dose-dependent manner as depicted by in vitro antioxidant assays. © 2022 SAAB
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.
Phylogenetic distribution, structural analysis and interaction of nucleotide excision repair proteins in cyanobacteria
(Elsevier B.V., 2023) Prashant R. Singh; Amit Gupta; Rajneesh; Jainendra Pathak; Rajeshwar P. Sinha
Cyanobacteria are photosynthetic Gram-negative, oxygen evolving prokaryotes with cosmopolitan distribution. Ultraviolet radiation (UVR) and other abiotic stresses result in DNA lesions in cyanobacteria. Nucleotide excision repair (NER) pathway removes the DNA lesions produced by UVR to normal DNA sequence. In cyanobacteria, detailed knowledge about NER proteins is poorly studied. Therefore, we have studied the NER proteins in cyanobacteria. Analyses of 289 amino acids sequence from 77 cyanobacterial species have revealed the presence of a minimum of one copy of NER protein in their genome. Phylogenetic analysis of NER protein shows that UvrD has maximal rate of amino acid substitutions which resulted in increased branch length. The motif analysis shows that UvrABC proteins is more conserved than UvrD, Further, UvrA with UvrB protein interacts with each other and form stable complex which have DNA binding domain on the surface of the complex. UvrB also have DNA binding domain. Positive electrostatic potential was found in the DNA binding region, which is followed by negative and neutral electrostatic potential. Additionally, the surface accessibility values at the DNA strands of T5-T6 dimer binding site were maximal. Protein nucleotide interaction shows the strong binding of T5-T6 dimer with NER proteins of Synechocystis sp. PCC 6803. This process repairs the UV-induced DNA lesions in dark when photoreactivation is inactive. Regulation of NER proteins protect cyanobacterial genome and maintain the fitness of organism under different abiotic stresses. © 2023 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).
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
Do cyanobacteria have enough mechanisms to counteract UV stress?
(Nova Science Publishers, Inc., 2017) Vidya Singh; Jainendra Pathak; Rajneesh; Richa; Deepak Kumar; Haseen Ahmed; Deepak K. Singh; Vinod K. Kannaujiya; Rajeshwar P. Sinha
Cyanobacteria are considered as major biomass producers and maintain the trophic energy dynamics of an ecosystem. They constitute the most promising group of photosynthetic microorganisms which produces an array of natural products of industrial importance 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 aroused serious concerns about its harmful consequences on all living organisms, including cyanobacteria. UVR adversely affects several physiological and biochemical processes in cyanobacterial cells and damage cellular DNA, either directly by interacting with certain biomolecules that absorb in the UV range, or indirectly, with the oxidative stress exerted by reactive oxygen species. However, to withstand the detrimental effects of solar UVR, cyanobacteria have evolved several lines of defense mechanisms, including avoidance, antioxidant production, synthesis of UV-absorbing/screening compounds, such as mycosporine-like amino acids (MAAs) and scytonemin, DNA repair, protein resynthesis and programmed cell death. This chapter deals with the effects of UVR on several biochemical and physiological processes of cyanobacteria and the various defense mechanisms developed by them against UVR stress. © 2017 Nova Science Publishers, Inc.
Purification, characterization and assessment of stability, reactive oxygen species scavenging and antioxidative potentials of mycosporine-like amino acids (MAAs) isolated from cyanobacteria
(Springer Science and Business Media B.V., 2022) Deepak K. Singh; Jainendra Pathak; Abha Pandey; Rajneesh; Vidya Singh; Rajeshwar P. Sinha
Mycosporine-like amino acids (MAAs) were characterized and their stability and free radical scavenging potentials were investigated in Anabaena sp. HKAR-7 and Fischerella sp. AR-5. UV/VIS absorption spectroscopy, high performance liquid chromatography and electrospray ionization-mass spectrometry showed occurrence of diverse forms of MAAs at retention time (RT) 1.16 (shinorine), 2.18 (mycosporine glycine-310) and 3.14 min (palythinol) with UVλmax 310, 332 and 334 nm respectively, in Fischerella sp. when contrasted with Anabaena sp. (prominent peak at RT 3.21 min (porphyra 334; P-334) with UVλmax 334 nm. MAAs showed dose-dependent in vitro antioxidative and in vivo reactive oxygen species (ROS) scavenging potentials. The MAA P-334 was used against strong allelochemical pyrogallic acid in Anabaena sp. P-334 reducing the negative impacts brought about by ROS, in this way, the malondialdehyde content and unwinding of dsDNA were similarly low. This clarifies the role of MAA P-334 against cell’s ROS under studied stressed conditions. © 2022, The Author(s), under exclusive licence to Springer Nature B.V.
Scytonemin Production by Cyanobacteria: A Threat To Algal Stromatolites in Salkhan Fossil Park, India
(Springer, 2025) Jainendra K. Pathak; Rajneesh; Vidya Singh; Neha Kumari; Rajeshwar Prasad Sinha
The present study concerns protection of important stromatolites on boulders in the Salkhan Fossil Park, Sonebhadra, India. Unfortunately, the fossils are at risk of biodegradation by rock-encrustations dominated by cyanobacteria. Some cyanobacteria have yellow-brown, lipophilic extracellular polysaccharide sheath pigment scytonemin that absorbs UV radiation and helps them to survive. Scytonemin, an evolutionary significant pigment, was extracted and purified from the surface of the stromatolite boulders. Genera including Scytonema sp., Lyngbya sp., and Aphanocapsa sp. were the most prevalent in these encrustations. Scytonemin was identified and characterized using fourier transform infrared (FTIR) spectroscopy, electro spray ionization-mass spectrometry (ESI-MS/MS), high-performance liquid chromatography (HPLC), and UV-Vis spectroscopy. With an absorption peak at 386 nm and a retention time of 1.45 min, scytonemin was found to be significantly present in the samples. Additionally, absorption was also observed at 252, 278, and 300 nm. In the FTIR spectrum, absorption was detected at 3421, 2940, 1027, and 1000–1320 cm−1. This compound’s identity as scytonemin was further confirmed by the ESI-MS/MS spectrum, displaying significant peaks at m/z 489, 517, 529, and 544. Scytonemin is a way to identify the presence of cyanobacterial colonization and its production enable them to cope with the harsh environmental conditions to survive in the rock incrustations. This biological issue is significant since it is related to the regrettable neglect of an important geological site, which is also a social and political issue. The biodegradation of the fossils at this park may be significantly influenced by the biological crusts that are rich in scytonemin. © The Author(s), under exclusive licence to ProGEO - International Association for the Conservation of Geological Heritage 2025.
In silico study on interaction between human polo-like kinase 1 and cyanobacterial sheath pigment scytonemin by molecular docking approach
(AMG Transcend Association, 2019) Jainendra Pathak; Soumila Mondal; Haseen Ahmed; Rajneesh; Shailendra P. Singh; Rajeshwar P. Sinha
Cancer is one of the major causes of death throughout the globe. It is expected that the number of new reports with cancer cases will reach twenty two million in the coming two decades. Africa, Central and South America and Asia will have more than 60 percent of the world’s new cancer reports and 70 percent of the world’s deaths from cancer will be contributed by these continents. Hence, drug discovery for treatment of cancer is the most worked area of this century. Polo-like kinase 1 (PLK-1) is highly expressed in human tumors and is important target of anti-cancerous drugs owing to its role in cell cycle events. It is crucial in maintenance of stability of genome and during different stages of mitosis. Scytonemin is a lipid-soluble and yellow-brown pigment exclusively synthesized by several cyanobacterial species in response to ultraviolet-A radiation. It functions as a photoprotective compound and can act as noncompetitive and competitive inhibitor of PLK-1. Other kinases such as Myt1, cyclin-dependent kinase 1/cyclin B, checkpoint kinase 1 and protein kinase C are also inhibited by scytonemin. In the present study, molecular docking approach has been employed for positioning the inhibitor (dimethoxyscytonemin) into the active site of PLK-1 for determining the most probable binding mode. Based on the docking studies, the models which are developed could be utilized for understanding the structure-activity relationships of the scytonemins and for the prescreening and designing of novel inhibitors of PLK-1. © 2019 by the authors.
Responses of a hot spring cyanobacterium under ultraviolet and photosynthetically active radiation: photosynthetic performance, antioxidative enzymes, mycosporine-like amino acid profiling and its antioxidative potentials
(Springer Science and Business Media Deutschland GmbH, 2021) Haseen Ahmed; Jainendra Pathak; Rajneesh; Piyush K. Sonkar; Vellaichamy Ganesan; Donat-P. Häder; Rajeshwar P. Sinha
This study summarizes the response of a hot spring cyanobacterium Fischerella sp. strain HKAR-14, under simulated light conditions of ultraviolet radiation (UVR), photosynthetically active radiation (PAR), PAR + UV-A (PA) and PAR + UV-A + UV-B (PAB). Exposure to UVR caused a decline in growth and Chl a while total carotene content increased under PA and PAB. Maximum photochemical efficiency of photosystem II (Fv/Fm) and relative electron transport rate decreased significantly in PA and PAB exposure. Higher non-photochemical quenching and lower photochemical quenching values were observed in UVR-exposed samples as compared to the control. Levels of intracellular reactive oxygen species (ROS) increased significantly in PAB and PA. Fluorescence microscopic images showed an increase in green fluorescence, indicating the generation of ROS in UVR. The antioxidant machinery including superoxide dismutase, catalase and peroxidase showed an increase of 1.76-fold and 2.5-fold superoxide dismutase, 2.4-fold and 3.7-fold catalase, 1.83-fold and 2.5-fold peroxidase activities under PA and PAB, respectively. High-performance liquid chromatography equipped with photodiode array detector, electrospray ionization mass spectrometry, Fourier-transform infrared spectroscopy and nuclear magnetic resonance spectroscopy analyses reveal the occurrence of a single mycosporine-like amino acid, shinorine (λmax 332.3 ± 2 nm, m/z 333.1), with a retention time of 1.157 min. The electrochemical characterization of shinorine was determined by cyclic voltammetry. The shinorine molecule possesses electrochemical activity and represents diffusion-controlled process in 0.1 M (pH 7.0) phosphate buffer. An antioxidant assay of shinorine showed its efficient activity as antioxidant which increased in a dose-dependent manner. © 2021, King Abdulaziz City for Science and Technology.

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