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 Effect of UV-B on enzymes of nitrogen metabolism in the cyanobacterium Nostoc calcicola(Elsevier GmbH, 1996) Ashok Kumar; Rajeshwar P. Sinha; Donat-P. HäderThe effects of ultraviolet-B (UV-B; 280-315 nm) irradiation on nitrogenase and nitrate reductase (NR) activity have been studied in the filamentous and heterocystous N2-fixing cyanobacterium Nostoc calcicola. Exposure of cultures to UV-B (5W/m2) for as little as 30 min caused complete inactivation of nitrogenase activity whereas nitrate reductase activity was stimulated twofold in comparison to one exposed to fluorescent white light. GS activity was also inhibited by UV-B treatment, but there was no total loss of activity even after 4 h. NR activity showed a gradual stimulation up to 4 h and thereafter it became constant. Stimulation was also obtained in reductant deficient cultures (12 h incubation in the dark) suggesting independence of NR of PS-II under UV-B. NR activity was also unaffected in the presence of DCMU, a known inhibitor of PS-II. However, both O2 evolution and 14CO2 uptake were completely abolished following 30 min of UV-B treatment. Addition of the protein synthesis inhibitor chloramphenicol (25 μg/ mL) to cultures did not show any inhibitory effect on NR activity. SDS-PAGE analysis of UV-B treated cultures elicited gradual loss of protein bands with increasing duration of exposure. Our findings suggest that UV-B irradiance has differential effects on the enzymes of the nitrogen metabolism in the cyanobacterium Nostoc calcicola. Further studies are needed to reveal the exact mechanism involved in the stimulation of NR activity by UV-B. Whether UV-B has a direct effect on NO2- accumulation in the cells needs detailed investigation.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 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.PublicationArticle Light-dependent impact of salinity on the ecophysiology of Synechococcus elongatus PCC 7942: Genetic and comparative protein structure analyses of UV-absorbing mycosporine-like amino acids (MAAs) biosynthesis(Elsevier B.V., 2021) Vinod Kumar; Soumila Mondal; Anjali Gupta; Pankaj K. Maurya; Rajeshwar P. Sinha; Donat-P. Häder; Shailendra P. SinghCyanobacteria are subjected to a dynamic light environment in their natural habitat or artificial cultivation system. The fluctuating light environment is associated with increased salinity stress due to the evaporation of the growth medium. Therefore, it is important to understand the physiology of the organisms under a dynamic environment of light and salinity which together affect the fitness and overall performance of the organism. We studied the growth behavior and other physiological parameters of Synechococcus elongatus PCC 7942 in the presence of different NaCl concentrations (0, 50, 100 and 200 mM) and light conditions such as low PAR (LPAR), high PAR (HPAR) and PAR + UVR using diurnal and continuous photoperiods. We also investigated the ability of S. elongatus PCC 7942 to biosynthesize UV-absorbing mycosporine-like amino acids (MAAs) and conducted genetic and comparative protein structure analyses to better understand its biosynthesis. Results obtained suggest that the impact of salinity stress caused by NaCl on growth behavior and physiological parameters such as photosynthetic pigments, the effective quantum yield of PSII and oxidative stress is dependent on the light environment. These parameters were affected differently by the quality and quantity of light and photoperiods, and the negative effect of salinity was alleviated by a high light environment. S. elongatus PCC 7942 does not biosynthesize MAAs due to the absence of MAAs biosynthesizing genes cluster in its genome. Results from genomic and comparative protein structure analyses suggested that DDGS and DHQS enzymes are different and DDGS but not DHQS is required for MAAs biosynthesis. Understanding the light-dependent impact of salinity stress may help in developing strategies for outdoor cultivation of cyanobacteria for bioenergy and valuable chemicals production by balancing absorbed and utilized radiant energy. © 2021 Elsevier B.V.PublicationBook Chapter Potential use of nuisance cyanobacteria as a source of anticancer agents(Elsevier, 2020) Hojun Lee; Stephen Depuydt; Soyeon Choi; Geonhee Kim; Youngdo Kim; Lalit K. Pandey; Donat-P. Häder; Taejun Han; Jihae ParkThe undesirable accumulation of cyanobacterial biomass, “green algal bloom, " has deleterious effects on the ecological stability of water bodies. It is equally notable that the huge cyanobacterial biomass can be used in the production of valuable biocommodities, including biofuels, functional food ingredients, UV-absorbing compounds, and pharmaceutical products. Cyanobacteria are known as a rich source of biopigments, fibers, antioxidants, vitamins, polysaccharides, mycosporin-like amino acids, proteins, and essential lipids. This review provides a summary on the various bloom-forming cyanobacterial species and their metabolites as a promising source of anticancer agents. © 2021 Elsevier Inc.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.PublicationBook Chapter Introduction(Elsevier, 2020) Rajeshwar Sinha; Donat-P. HäderGlobalization, increasing resistance of parasites to existing drugs and an aging world population, has generated a need for the development of novel drugs. Till now, a relatively low number of bioactive compounds are being used in prescription drugs. These compounds are often chemically related to each other. Therefore, there is a constant need for new therapeutic compounds by uncovering new bioactive compounds that have the potential to be developed further into drugs. Microorganisms such as bacteria, fungi, microalgae, and cyanobacteria have proven to be an excellent, but still underexplored source for bioactive compounds. Traditionally, novel compounds produced by these microorganisms were discovered via conventional bioprospecting based on the isolation of potential producers and screening their extracts in a variety of bioassays. Over time, most of the natural products identifiable by this approach were discovered, and the pipeline for new drugs based on metabolites produced by microbes started to run dry. Despite great efforts to generate synthetic drugs, only 27% of the approved drugs in medicine are of completely synthetic origin. Most of the drugs that are currently being used in the clinic are derived from natural products. For over several decades, microbes served as a valuable source of bioactive natural products some of which were eventually developed into drugs to treat cancer, infections, and immune system-related diseases. Hence, these bioactive compounds hold a promising future in pharmaceutical research and have tremendous applications in the field of biotechnology and new drug discovery. © 2021 Elsevier Inc.PublicationArticle 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. SinhaScytonemin 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. © 2019PublicationArticle Impacts of ultraviolet radiation on certain physiological and biochemical processes in cyanobacteria inhabiting diverse habitats(Elsevier B.V., 2019) Rajneesh; Jainendra Pathak; Richa; Donat-P. Häder; Rajeshwar P. SinhaCertain physiological and biochemical processes of Fischerella sp. strain HKAR-13 and Nostoc sp. strain HKAR-2 isolated from paddy field and hot spring respectively were studied in response to ultraviolet radiation (UVR). Cultures were irradiated under varying combinations of UV-B, UV-A and photosynthetically active radiation (PAR). Significant decrease in chlorophyll a content was observed in Nostoc sp. strain HKAR-2 (19.31 to 4.08 μg/gfw) and Fischerella sp. strain HKAR-13 (13.55 to 3.40 μg/gfw) after 72 h of PAR + UV-A + UV-B (PAB) treatment. Total carotene content increased upto 36 h where as phycocyanin content decreased as exposure time increased in both the cyanobacteria. Photosystem II (PSII) activity decreased to about 88% and 93% in Nostoc sp. strain HKAR-2 and Fischerella sp. strain HKAR-13 respectively. Antioxidative activities of superoxide dismutase and catalase increased to 1.8–6.0 fold after 48 h of UVR exposure as compared to non-irradiated cultures. Additionally, Fischerella sp. strain HKAR-13 was also able to synthesize scytonemin that carry out UV-screening but its synthesis was not observed in Nostoc sp. strain HKAR-2. UVR also resulted in 3–5 fold increase in reactive oxygen species in Fischerella sp. strain HKAR-13 and 2.0–4.5 fold increase in Nostoc sp. strain HKAR-2. Significant decrease in ds DNA content and increase in malondialdehyde content was observed in both cyanobacterial strains. These results revealed that combined effects of UV-A + UV-B was more deleterious than UV-A and UV-B alone and Fischerella sp. strain HKAR-13 was more prone to UVR as compared to Nostoc sp. strain HKAR-2, a hot spring isolate. The more resistant cyanobacterium Nostoc sp. strain HKAR-2 can be used as inoculant in desert soil and production of various value added products. © 2018 Elsevier B.V.PublicationBook Chapter Mechanisms of Photoprotection in Cyanobacteria(Elsevier, 2018) Jainendra Pathak; Haseen Ahmed; Prashant R. Singh; Shailendra P. Singh; Donat-P. Häder; Rajeshwar P. SinhaCyanobacteria 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.
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