Comparative study of natural and synthetic phenolic compounds as efficient laccase mediators for the transformation of cationic dye

Laccase mediator systems are important bioremediation agents as the rate of reactions could be enhanced in the presence of the mediators. In the present study commercial laccase was used for the biotransformation of malachite green (MG), a cationic dye in the presence of phenolic compounds of groundnut shells and lignin-related synthetic redox mediators. The addition of ethanolic phenolic extract of groundnut shell enhanced the decolorization of MG from 38.73 to 87.32%. All the selected natural phenolic compounds enhanced the decolorization of MG like synthetic mediator 1-hydroxybenzotriazole. Characterization of MG transformation products by UV-vis and HPLC analyses revealed that N-demethylation was the key mechanism of decolorization of MG by laccase alone as well as in the presence some of redox mediators. But in case of MG decolorization with laccase mediated system by groundnut shell extract and other natural compounds, leuco-malachite green was the major transformed product. Growth inhibition test based on mycelial growth inhibition of white rot fungus Phanerochaete chrysosporium (ATCC 1556) revealed that treatment with laccase plus natural and synthetic mediators effectively reduced the growth inhibitory levels of MG than that of control. Thus, the study revealed that the natural phenolic compounds could be used as potential redox mediators for enhanced laccase-mediated decolorization of malachite-green dye. (C) 2011 Elsevier B.V. All rights reserved.