S. Arun

Bio: S. Arun is an academic researcher from Alagappa University. The author has contributed to research in topics: Glutathione peroxidase & Lipid peroxidation. The author has an hindex of 10, co-authored 14 publications receiving 939 citations. Previous affiliations of S. Arun include Spanish National Research Council & Bharathidasan University.

Antioxidant enzyme activities and lipid peroxidation in the freshwater cladoceran Daphnia magna exposed to redox cycling compounds.

Abstract: Contaminant-related changes in antioxidative processes in the freshwater crustacea Daphnia magna exposed to model redox cycling contaminant were assessed. Activities of key antioxidant enzymes including catalase, superoxide dismutase, glutathione peroxidase and glutathione S-transferases and levels of lipid peroxidation measured as thiobarbituric acid-reactive substances (TBARS) and lipofucsin pigment content were determined in D. magna juveniles after being exposed to sublethal levels of menadione, paraquat, endosulfan, cadmium and copper for 48 h. Results denoted different patterns of antioxidant enzyme responses, suggesting that different toxicants may induce different antioxidant/prooxidant responses depending on their ability to produce reactive oxygen species and antioxidant enzymes to detoxify them. Low responses of antioxidant enzyme activities for menadione and endosulfan, associated with increasing levels of lipid peroxidation and enhanced levels of antioxidant enzyme activities for paraquat, seemed to prevent lipid peroxidation, whereas high levels of both antioxidant enzyme activities and lipid peroxidation were found for copper. For cadmium, low antioxidant enzyme responses coupled with negligible increases in lipid peroxidation indicated low potential for cadmium to alter the antioxidant/prooxidant status in Daphnia. Among the studied enzymes, total glutathione peroxidase, catalase and glutathione S-transferase appeared to be the most responsive biomarkers of oxidative stress.

Changes in antioxidant enzyme activities, fatty acid composition and lipid peroxidation in Daphnia magna during the aging process.

Abstract: Age-related changes in the balance between endogenous pro-oxidative and antioxidative processes in the freshwater cladoceran Daphnia magna (Crustacea) were assessed. The activities of key antioxidant enzymes including catalase, superoxide dismutase and glutathione peroxidase and levels of lipid peroxidation measured as thiobarbituric acid-reactive substances (TBARS) were determined in eight age classes, covering juvenile, young and senescent adults. Age-related changes in fatty acid composition were also measured to examine the contribution of polyunsaturated fatty acids (PUFA) in the peroxidation status of animals. Biochemical responses depicted in this study demonstrated that age-related decline in survival was accompanied by increasing oxidative stress and oxidative damage. Enhanced oxidative stress in aging D. magna was suggested by the significant increase in the formation of lipid peroxides, and a concomitant reduction of unsaturated fatty acids of 20 or more carbon atoms. Because aging was accompanied by selective loss of key antioxidant enzymes and small changes in the amount of PUFA, the breakdown of antioxidant defences might have directly contributed to oxidative stress, membrane lipid peroxide and a decline of survival. Indeed, the results reported here, indicate that age-related increases of lipid peroxides were at least partially due to the functional imbalance of enzymatic antioxidant defences.

Antioxidant enzymes in freshwater prawn Macrobrachium malcolmsonii during embryonic and larval development

Abstract: Activities of superoxide dismutase, catalase, glutathione peroxidase (selenium-dependent and selenium-independent) and glutathione- S -transferases were analysed in freshwater prawn Macrobrachium malcolmsonii during embryonic and larval development. An elevated level of these enzymes was encountered in the larval stage of M. malcolmsonii when compared to its preceding embryonic stages. Enzyme activities were also analysed in hepatopancreas, muscle and gill of M . malcolmsonii sub-adults and the highest activity was observed in hepatopancreas. This result is in agreement with the notion that hepatopancreas is the major metabolic centre for production of reactive oxygen species in crustaceans.

Exoelectrogenic bacteria that power microbial fuel cells

Abstract: The use of microbial fuel cells to generate electrical current is increasingly being seen as a viable source of renewable energy production In this Progress article, Bruce Logan highlights recent advances in our understanding of the mechanisms used by exoelectrogenic bacteria to generate electrical current and the important factors to consider in microbial fuel cell design There has been an increase in recent years in the number of reports of microorganisms that can generate electrical current in microbial fuel cells Although many new strains have been identified, few strains individually produce power densities as high as strains from mixed communities Enriched anodic biofilms have generated power densities as high as 69 W per m2 (projected anode area), and therefore are approaching theoretical limits To understand bacterial versatility in mechanisms used for current generation, this Progress article explores the underlying reasons for exocellular electron transfer, including cellular respiration and possible cell–cell communication

Microbial Biofilm Voltammetry: Direct Electrochemical Characterization of Catalytic Electrode-Attached Biofilms

Abstract: While electrochemical characterization of enzymes immobilized on electrodes has become common, there is still a need for reliable quantitative methods for study of electron transfer between living cells and conductive surfaces. This work describes growth of thin (<20 microm) Geobacter sulfurreducens biofilms on polished glassy carbon electrodes, using stirred three-electrode anaerobic bioreactors controlled by potentiostats and nondestructive voltammetry techniques for characterization of viable biofilms. Routine in vivo analysis of electron transfer between bacterial cells and electrodes was performed, providing insight into the main redox-active species participating in electron transfer to electrodes. At low scan rates, cyclic voltammetry revealed catalytic electron transfer between cells and the electrode, similar to what has been observed for pure enzymes attached to electrodes under continuous turnover conditions. Differential pulse voltammetry and electrochemical impedance spectroscopy also revealed features that were consistent with electron transfer being mediated by an adsorbed catalyst. Multiple redox-active species were detected, revealing complexity at the outer surfaces of this bacterium. These techniques provide the basis for cataloging quantifiable, defined electron transfer phenotypes as a function of potential, electrode material, growth phase, and culture conditions and provide a framework for comparisons with other species or communities.