Biodegradation of synthetic dye using partially purified and characterized laccase and its proposed mechanism

The supernatant obtained from the extracellular laccase produced by Phanerochaete chrysosporium was used as the enzyme source to conduct a partial purification, characterization and dye decolorization study. The partially purified enzyme was stable in the pH range of 3–5 and showed an optimum activity at pH 4.0, using guaiacol as a substrate. Laccase stability of pH was determined and discovered to retain 100% of its activity at a pH of 4.0 after 2 h. The maximum enzyme activity was obtained between 30 and 50 °C. The maximum velocity and Michaelis constant were calculated as 3.171 µM −1 ·min and 1628.23 µM, respectively. The enzyme was activated by Fe 2+ , Zn 2+ , Ca 2+ and Cu 2+ , while Hg 2+ , Mn 2+ , Co 2+ , Mg 2+ , Cd 2+ , Ni 2+ reduced the laccase activity. The partially purified enzyme was strongly inhibited by 1 mM of NaN 3 and sodium thioglycolate. Among the eight different dyes (Malachite green, Safranin, Crystal violet, Methylene blue, Eriochrome black T, Methyl red, Methyl orange, Rhodamine B and Nigrosin), the enzyme showed highly efficient decolorizing activity (99%) toward Malachite green after treatment for 24 h at 30 °C. Antibacterial results showed that the product obtained by treating the dye with the enzyme is completely non-toxic to Staphylococcus aureus , Pseudomonas aeruginosa and Escherichia coli . High-performance liquid chromatography and mass spectroscopy analysis of the extracted product confirmed the complete biodegradation of Malachite green and Leucomalachite green. Di-benzyl methane and 4-(dimethylamino) benzaldehyde were the ultimate products identified in this research.