Department of Biological Sciences
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Item Hepatotoxicity of Microcystis aeruginosa Strains Growing as Blooms in Certain Eutrophic Ponds(TUD, 2006) Jha, Prabhat N.; Kumar, AnilCritical assessment of five eutrophicated ponds of Varanasi city (India) revealed the presence of heavy blooms of cyanobacteria consisting mainly of Microcystis aeruginosa. Crude aqueous extracts of blooms as well as laboratory grown M. aeruginosa isolated from three ponds, namely Lakshmikund, Durgakund and Adityanagar showed toxicity in mouse bioassay test. Crude aqueous extracts from these samples caused death of test mice within 1h of administration (i.p.) with a LD50 of 60 mg/kg body weight and the treated animals showed clinical signs of hepatotoxicity. However such an effect was not associated with the blooms from Laatbhairov and Surajkund ponds suggesting that not all strains of M. aeruginosa are toxic. Based on spectral properties (?max 230 nm), and comparison with standard microcystin-LR, the toxin is tentatively identified as microcystin-LR. The purified toxin caused death of test mice within 40 min of its administration with a LD50 of 100 µg/ kg body weight and induced gross morphological and functional changes in liver. A 1.55 fold increase in liver weight accompanied by deep red coloration most probably due to hemorrhage and blood pooling suggested the hepatotoxic properties of the toxin. Hepatotoxicity was also evident from the drastic increase (up to 2.5 fold) in activity of serum enzymes such as glutamate pyruvate transaminase/alanine aminotransferase (GPT/ALT), lactate dehydrogenase (LDH) and alkaline phosphatase (APase) following toxin treatment. ^14C-labelling experiments demonstrated maximum accumulation (~15%) of ^14C- toxin after 20 min. of toxin administration. Appreciable level of toxin was also detected in water of four ponds. In conclusion these results clearly demonstrate that microcystin-producing blooms of M. aeruginosa are common in eutrophicated ponds of Varanasi city but not all ponds harbour toxic blooms.Item Click chemistry inspired synthesis of piperazine-triazole derivatives and evaluation of their antimicrobial activities(Springer, 2015) Jha, Prabhat N.; Kumar, AnilA series of novel piperazine-1,2,3-triazole derivatives, which entailed the bioisosteric replacement of the imidazole moiety and hybridization of two drug scaffolds was prepared by employing the regioselective copper (I)-catalysed azide-alkyne 1,3-dipolar cycloaddition reaction. The synthesized compounds were evaluated for antibacterial activities against Gram-negative (E. Coli and P. Putida), Gram-positive S. Aureus bacteria and fungicidal activities against F. oxysporum, F. gramillarium and F. monalliforme fungi. Compound 7ac′ exhibited moderate but promising antibacterial activity against Gram-negative bacteria and fungicidal activity against F. oxysporum and F. gramillarium.Item Biochemistry and genetics of ACC deaminase: a weapon to “stress ethylene” produced in plants(Frontiers, 2015-09) Jha, Prabhat N.; Kumar, Anil1-aminocyclopropane-1-carboxylate deaminase (ACCD), a pyridoxal phosphate-dependent enzyme, is widespread in diverse bacterial and fungal species. Owing to ACCD activity, certain plant associated bacteria help plant to grow under biotic and abiotic stresses by decreasing the level of “stress ethylene” which is inhibitory to plant growth. ACCD breaks down ACC, an immediate precursor of ethylene, to ammonia and α-ketobutyrate, which can be further metabolized by bacteria for their growth. ACC deaminase is an inducible enzyme whose synthesis is induced in the presence of its substrate ACC. This enzyme encoded by gene AcdS is under tight regulation and regulated differentially under different environmental conditions. Regulatory elements of gene AcdS are comprised of the regulatory gene encoding LRP protein and other regulatory elements which are activated differentially under aerobic and anaerobic conditions. The role of some additional regulatory genes such as AcdB or LysR may also be required for expression of AcdS. Phylogenetic analysis of AcdS has revealed that distribution of this gene among different bacteria might have resulted from vertical gene transfer with occasional horizontal gene transfer (HGT). Application of bacterial AcdS gene has been extended by developing transgenic plants with ACCD gene which showed increased tolerance to biotic and abiotic stresses in plants. Moreover, distribution of ACCD gene or its homolog's in a wide range of species belonging to all three domains indicate an alternative role of ACCD in the physiology of an organism. Therefore, this review is an attempt to explore current knowledge of bacterial ACC deaminase mediated physiological effects in plants, mode of enzyme action, genetics, distribution among different species, ecological role of ACCD and, future research avenues to develop transgenic plants expressing foreign AcdS gene to cope with biotic and abiotic stressors. Systemic identification of regulatory circuits would be highly valuable to express the gene under diverse environmental conditions.Item Design and Synthesis of Imidazo/Benzimidazo[1,2-c]quinazoline Derivatives and Evaluation of Their Antimicrobial Activity(ACS, 2018) Jha, Prabhat N.; Kumar, AnilA new class of fused quinazolines has been designed and synthesized via copper-catalyzed Ullmann type C–N coupling followed by intramolecular cross-dehydrogenative coupling reaction in moderate to good yields. The synthesized compounds were tested for in vitro antibacterial activity against three Gram negative (Escherichia coli, Pseudomonas putida, and Salmonella typhi) and two Gram positive (Bacillus subtilis, and Staphylococcus aureus) bacteria. Among all tested compounds, 8ga, 8gc, and 8gd exhibited promising minimum inhibitory concentration (MIC) values (4–8 μg/mL) for all bacterial strains tested as compared to the positive control ciprofloxacin. The synthesized compounds were also evaluated for their in vitro antifungal activity against Aspergillus niger and Candida albicans and compounds 8ga, 8gc, and 8gd having potential antibacterial activity also showed pronounced antifungal activity (MIC values 8–16 μg/mL) against both strains. The bactericidal assay by propidium iodide and live–dead bacterial cell screening using a mixture of acridine orange/ethidium bromide (AO/Et·Br) showed considerable changes in the bacterial cell membrane, which might be the cause or consequence of cell death. Moreover, the hemolytic activity for most potent compounds (8ga, 8gc, and 8gd) showed their safety profile toward human blood cells.Item A straightforward TBHP-mediated synthesis of 2-amidobenzoic acids from 2-arylindoles and their antimicrobial activity(RSC, 2019) Jha, Prabhat N.; Kumar, AnilA simple and highly efficient strategy has been developed for the synthesis of 2-amidobenzoic acids through the tert-butyl hydroperoxide (TBHP)-mediated oxygenation and sequential ring opening of 2-arylindoles in a one-pot fashion under metal-free aerobic conditions. The developed synthetic protocol is operationally simple, tolerates a wide range of functional groups, and is amenable to the gram-scale. Radical trapping experiments revealed that the reaction involves a radical pathway. The synthesized compounds (2a–s) were tested for in vitro antimicrobial activity. Among all screened compounds, 2d showed the maximum antibacterial activity against P. aerugunosa (ZOI = 17 mm, MIC = 32 μg mL−1) and compounds 2d and 2p showed the maximum (32 μg mL−1) antifungal activity against A. flavus and C. albicans.