Catalyzed Mediator-Based Decolorization of Five Synthetic Dyes by Pleurotus ostreatus ARC280 Laccase

Abstract

Aim: The aim of the present study was to evaluate qualitatively the decolorization of five dyes by Pleurotus ostreatus (P. ostreatus) ARC280 using solid medium. The laccase produced by the fungus was used in terms of its concentration and thermal stability for enzymatic decolorization and also in combination with Hydroxybenzotriazole (HBT) as a redox mediator. Study Design: Qualitative evaluation of decolorization of dyes and determining the best conditions required for decolorization in the presence and absence of HBT. Place and Duration of Study: Department of Microbial Chemistry, Genetic Engineering and Biotechnology Division, National Research Centre (NRC), Cairo, Egypt, between January 2013 and February 2014. Methodology: P. ostreatus ARC280 fungal ability for dyes decolorization was qualitatively evaluated on solid medium containing (g/L): dye, 0.1; glucose, 10; agar, 30; 100 mL mineral solution and 100 mL wheat bran washing water obtained by boiling 50 g of wheat bran in 1000 mL of distilled water. The efficiency of decolorization was expressed in terms of decolorization percentage as follows: Decolorization (%) = 100 × Absorbance t0 - Absorbance tf   Absorbance t0 Where Absorbance t0 is the absorbance at the optimum wavelength of the reaction mixture before incubation with the enzyme and Absorbance tf is the absorbance at the optimum wavelength after incubation time. Results: The enzyme was efficient in decolorizing Acid Blue C.I. 220 (100%), Dichlorophenol indophenol sodium salt D 5110 (92.6%) and Brilliant Green C.I. 42040 (78.6%) after 6 h of incubation at 30ºC. In the presence of HBT (1 mM), Lanasol Red 6G was greatly affected by HBT as a laccase mediator system with decolorization percentage of 53.85% instead of 10.90 in case of laccase alone, however the enzyme could not efficiently decolorize Foron Yellow Brown S 2RFLI dye even in presence of HBT. The decolorization efficiency of all dyes was decreased by increasing reaction temperature from 30 to 50ºC. The absorbance reduction at the maximum wavelength was recorded with all the tested dyes. Conclusion: The results obtained clearly confirmed the role of P. ostreatus ARC280 laccase and its mediated system in the decolorization of structurally different dyes.