Enzyme activities and decolourization of single and mixed azo dyes by the white-rot fungus Phanerochaete chrysosporium

Abstract

Decolourization of two azo dyes, namely Direct Red–80 (DR–80) and Mordant Blue–9 (MB–9), by Phanerochaete chrysosporium was investigated both individually and in mixtures in batch shake flasks. Mixture experiments containing these dyes were performed at five different initial concentrations ranging from 10 to 200 mg l −1 each. While the results of dye decolourization in mixture indicated decolourization efficiencies of more than 92%, the efficiencies were more than 94% in the single dye system. During the experiments, enzyme activities of lignin peroxidase (LiP) and manganese peroxidase (MnP) were also analyzed. Maximum LiP and MnP activities of 136 U l −1 and 16 U l −1, respectively, were achieved after 24 h of the fungal culture for respective initial DR–80 concentrations of 10 mg l −1 and 150 mg l −1 in the single dye system. In case of MB–9, maximum enzyme activities were 118 U l −1 (LiP) and 34 U l −1 (MnP) at initial concentrations of 50 mg l −1 and 100 mg l −1, respectively. When the two dyes were added together to the culture, maximum LiP and MnP activities were found to be 139 U l −1 and 132 U l −1 respectively for an initial concentration combination of 50 mg l −1 DR–80 and 10 mg l −1 MB–9. These profiles of enzyme activities and dye decolourization by the fungus, in both single and mixed dye systems, suggest the fungal peroxidase enzymes play a strong role in dye decolourization.