Abstract
A novel laccase-producing white-rot fungus, Marasmius sp. BBKAV79 (Genbank Accession Number-KP455496, KP455497), was isolated and subjected to purification, characterization and dye decolorization study. The purified enzyme was obtained with a specific activity of 0.226 U mg−1 protein and a final yield of 13.5 %. The enzyme was found to be a monomeric protein with a molecular mass of ~75 kDa as estimated by non-denaturing polyacrylamide gel electrophoresis (PAGE) and further confirmed with zymogram analysis. The optimal pH and temperature of the laccase was recorded to be 5.5 and 40 °C, respectively. The metal ions Hg2+ and Ag+ were found to drastically inhibit the activity of laccase at the rate of 96.6 and 96.5 %, respectively. Nevertheless, Fe3+ was found to inhibit laccase activity at 40 %. Phenylmethanesulfonyl fluoride (PMSF) strongly inhibited the laccase activity, and additives viz, sodium dodecyl sulfate (SDS), hydrogen peroxide (H2O2) and sodium chloride (NaCl) were known to follow the earlier pattern of enzyme inhibition. The values of kinetic parameters K m and V max for purified laccase were noted at 3.03 mM and 5 μmol min−1, respectively, for guaiacol as substrate. The textile dyes were decolorized at a range of 72–76 % and 88–93 % when treated with Marasmius sp. BBKAV79 and purified laccase, respectively. Based on the outcome of the present investigation, it could be, therefore, inferred that laccase isolated from Marasmius sp. BBKAV79 effectively decolorizes the textile dyes; however, the metal ions Hg2+, Ag+ and Fe3+ and agents like PMSF, SDS, H2O2 and NaCl pose an effective inhibitory potential under specified physicochemical conditions.
Highlights
Relentless production, utilization and dumping of synthetic organic chemicals has contributed to environmental pollution globally (David and Kartheek 2015; Malaja et al 2014)
The textile dyes were decolorized at a range of 72–76 % and 88–93 % when treated with Marasmius sp
Organism screening for laccase-producing microbes on potato dextrose agar (PDA) plates containing indicators resulted in isolation of eight fungal strains
Summary
Relentless production, utilization and dumping of synthetic organic chemicals has contributed to environmental pollution globally (David and Kartheek 2015; Malaja et al 2014). Synthetic dyes are one such class of chemicals that are broadly used in wide range of industries including textile, paper, printing, cosmetics and pharmaceuticals (Vinodhkumar et al 2013). Many synthetic dyes are difficult to decolorize due to their complex structure. Decolorization of textile dye effluent does not occur when treated aerobically by municipal sewage systems (Willmott et al 1998). Watersoluble, reactive and acid dyes are the most problematic, as they tend to pass through conventional treatment systems unaffected (Willmott et al 1998). Color can be removed from effluent by chemical and physical methods including adsorption, coagulation–flocculation, ion exchange, oxidation and electrochemical methods (Lin and Peng 1994, 1996).
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