Scholarly Publications
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This community showcases the academic contributions of faculty and researchers at Banaras Hindu University (BHU) and provides a year-wise compilation of publications across disciplines. Institutional Repository BHU
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PublicationArticle 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 SinhaThe 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.PublicationBook Chapter Bioprospection of Photoprotective Compounds from Cyanobacteria(Springer Nature, 2023) Prashant R. Singh; Ashish P. Singh; Rajneesh; Amit Gupta; Rajeshwar P. Sinha; Jainendra PathakCyanobacteria are one of the oldest photosynthetic nitrogen fixers of the terrestrial as well as aquatic ecosystems. Cyanobacteria and microalgae produce a large number of secondary metabolites having biomedical, industrial, and biotechnological importance. Due to their presence in vast habitats, cyanobacteria and microalgae were exposed to variety of harsh environmental factors such as salt, desiccation, temperature, heavy metals, and ultraviolet radiation (UVR). In response, cyanobacteria have developed different mechanisms to cope these harsh environmental conditions. Photosynthetic nature of cyanobacteria continuously exposes them to lethal doses of UVR coming with solar radiation which affects their physiology, photosynthetic efficiency, productivity by reactive oxygen species (ROS) generation inside the cell and ultimately leads to cell death. In response to these stresses cyanobacteria have developed different protective mechanisms such as avoidance, enzymatic and non-enzymatic defence system and synthesis of novel secondary metabolites such as mycosporine-like amino acids (MAAs) and scytonemin. MAAs are water-soluble molecules that absorb short wavelength of solar UVR which release the energy in the form of heat. Scytonemin is a small hydrophobic alkaloid pigment present in the extracellular sheath of some cyanobacteria that acts as UVR protectant. Scytonemin and MAAs are highly photostable therefore, they primarily function as UV-screening compounds. They also show antioxidative properties. The capability of cyanobacteria to produce large number of secondary metabolites which serve as natural sunscreens, antibiotic, antifungal, anticancer and antiviral agents make them economically important organisms. These are readily biotechnologically exploitable in the cosmetics and other industrial sectors for the creation of novel medications and drugs. Hence, bioprospection of these photoprotective compounds and other secondary metabolites from cyanobacteria and microalgae becomes crucial. © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023.PublicationArticle 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. SinhaCyanobacteria 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.PublicationArticle 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. SinhaCyanobacteria 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.PublicationArticle 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. SinhaPhotolyases (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).PublicationArticle 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. SinhaMycosporine-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 SAABPublicationArticle 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. SinhaMycosporine-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.PublicationArticle 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. SinhaThis 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.PublicationBook Chapter Ultraviolet-screening compound mycosporine-like amino acids in cyanobacteria: biosynthesis, functions, and applications(Elsevier, 2020) Deepak K. Singh; Jainendra Pathak; Abha Pandey; Vidya Singh; Haseen Ahmed; Rajneesh; Deepak Kumar; Rajeshwar P. SinhaPhotosynthetic efficiency of photoautotrophs such as algae, cyanobacteria, and higher plants is severely affected by the solar ultraviolet (UV) radiation (UVR), but the mechanisms/strategies employed by these photoautotrophs, including cyanobacteria, against lethal UVR exposure are still not well understood. On exposure to UVR, cellular damage is triggered directly by affecting proteins and DNA as well as indirectly via the generation of damaging doses of reactive oxygen species (ROS). For their survival and sustenance and overcoming the harmful effects of UVR, cyanobacteria synthesize their own UV-blockers such as mycosporine-like amino acids (MAAs) and scytonemin, which help in protecting them against UVR. MAAs are low molecular weight (<400Da), water-soluble nitrogenous compounds having maximum absorption in the UV range (310–360nm). Their structure consists of a cyclohexenimine or cyclohexenone ring attached to an amino acid, amino alcohol, or an amino group. However, the precise biosynthetic route of these multipurpose compounds is still unclear. Evidence suggests their origin from the pentose phosphate pathway as well as from the shikimate pathway with 4-deoxygadusol acting as a common precursor of all types of MAAs. Photochemical and photophysical studies evidenced that MAAs absorb UVR and release it as heat, without generation of free radicals. In addition, MAAs also contribute to several other physiological functions, such as scavengers of harmful ROS, as an antioxidant and even in osmoprotection. Hence, MAAs offer tremendous potential for the development of novel UV-sunscreens owing to their direct and indirect photoprotective properties. These characteristics make MAAs a promising source of natural sunscreen, having cosmetic and pharmaceutical applications. This chapter focuses on the distribution, biosynthesis, functions, and applications of this economically and ecologically important compound along with recent advances made in this field of study. © 2020 Elsevier Inc. All rights reserved.PublicationBook Chapter Cyanobacterial photoprotective compounds: Characterization and utilization in human welfare(Elsevier, 2020) Rajeshwar P. Sinha; Jainendra Pathak; Rajneesh; Haseen Ahmed; Abha Pandey; Prashant R. Singh; Sonal Mishra; Donat-P. HäderIn recent decades, numerous bioactivities of cyanobacterial photoprotective compounds such as carotenoids, mycosporine-like amino acids (MAAs), scytonemin, and phycobilin proteins have been reported. Although the time taken for clinical trials of natural compounds for human use might be more than 50 years, these natural pharmacophores have several advantages over synthetic ones including less toxicity. Moreover, sourcing of cyanobacteria can be sustainable in marine systems owing to their fast biomass turnover rates. These cyanobacterial bioactive compounds impart several health-promoting properties such as antioxidant, antiaging, and antiproliferative effects upon crucial application to humans besides their distinct physiological roles, hence, making them suitable for use in cosmetics. The cosmeceutical industry has grown significantly since the last decade, with an annual growth of 7.7% from 2012 to 2016. Considering the recent advancements in the algal research, these cyanobacterial bioactive photoprotective compounds will be a major contender in the cosmeceutical industry. Here, we present an overview of the structure, genetics, biosynthesis, and applications of the cyanobacterial photoprotective compounds MAAs and scytonemin. The information summarized in this chapter can be utilized in designing projects targeting commercial production of these cyanobacterial photoprotective bioactive compounds for human welfare. © 2021 Elsevier Inc.
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