Biodegradation of Malachite Green by the Ligninolytic Fungus Aspergillus flavus

The azo class of synthetic dyes represents one of the most industrially used dyes as well as a major class of environmental contaminants, which possess one or more azo bonds (-N=N-) along with aromatic rings and sulfonic groups. Due to its recalcitrant nature and toxicity for animals and human beings, the elimination of these dyes from the environment is essential. The present study focuses on the biodegradation of such azo dye, malachite green (MG), through a potent ligninolytic fungus, Aspergillus flavus (F10). A. flavus (F10) completely decolorized MG (150mgL(-1)) within 6-8 days in optimized Kirk's basal medium under static aerobic conditions at pH 5.8. Sucrose and sodium nitrate were efficient carbon and nitrogen sources, respectively. The products obtained after degradation were examined using UV-vis spectrophotometry, Fourier transform IR spectroscopy, and liquid chromatography-mass spectroscopy. The metabolic intermediate products were identified as N-demethylated and N-oxidized metabolites, including primary and secondary arylamines, which confirms the involvement of laccase and manganese peroxidase in decolorization and degradation of MG. The end products of MG degradation were nontoxic. A. flavus (F10), immobilized by entrapment on natural and synthetic polymeric matrices was found to be a more efficient degrader of MG as compared to free cells.