KINETICS OF BIODEGRADATION OF SYNTHETIC DYES BY AGARICUS SPECIES

Abstract

Textile dyes have always been considered in the context of recalcitrant xenobiotics compounds in water and soil ecology. Present research work was focused on the bioremediation potential of Agaricus species to decolorize and to detoxify the different synthetic dyes and dye containing effluents. The purification, characterization, kinetics & thermodynamic studies of ligninolytic enzymes produced by the fungi during dye decolorization process, were also performed. Complete (100%) removal of NOVASOL Direct Black and 83.34 % Reactive Black by Agaricus bitorqus A66 & Agaricus bisporus A21 were attained by optimizing optimal conditions like media composition, pH, temperature, inoculum size, carbon and nitrogen supplements, metal ions, redox mediators and dye concentration. In the entire processes of optimization of decolorization lignin peroxidase (LiP) was the major enzyme with minor activities of MnP and laccase when the decolorization of Novasol black was carried out by Agaricus bitorqus A66 and manganese peroxidase (MnP) was the main enzyme with minor LiP and laccase activities in case of reactive black treated by Agaricus bisporus A21. As highly efficient decolorization (100%) of synthetic dye was attained by these Agaricus species in a reasonably short period of time under optimum conditions, these were therefore, applied to check out their potential application in the decolorization of different practical/real textile industry effluent. It was observed that complete (100%) and 95.66 % decolorization of Navy blue colored effluent was achieved by Agaricus bitorqus and Agaricus bisporus A21 , respectively under optimum conditions. To access the water quality parameters, the treated and untreated effluent samples were analyzed to determine COD, BOD, TSS and TDS. The fungal treated effluents were less polluted as compared to original industrial effluents. The enzymes (LiP & MnP) produced under optimum decolorization conditions were purified to 1.54 & 6.9 fold with % yield of 6.74 and 8.48, respectively by ammonium sulfate precipitation, followed by three purification steps including, Dialysis, gel-filtration and anion- exchange chromatography. MnP and LiP secreted by respective fungi displayed optimum activities pH 7.0 & 6.0 and at 45 &400C, respectively. The Km values for veratryl alcohol and MnSO4 were 16.67 mM, 3.33 mM for MnP and LiP, having Vmax values of 179.17 and 231.00 mM, respectively. Thermodynamic and activation parameters provide a detailed mechanism for many chemical and biological reactions. The kinetic and thermodynamic characterization revealed Gibbs free energy ΔG* values for denaturation of MnP and LiP as 272.12 & 272.6 KJmol-1, enthalpy of thermal unfolding ΔH* of transition state was 39.91& 72.83 KJmol-1 and entropy of thermal unfolding (ΔS*) was -707.94 &, -609 Jmol-1K-1 at 50oC along with activation energy for inactivation of Ea 42.6, 75.6 KJmol-1, respectively.