Enhancing catalytic functionality of Trametes versicolor IBL-04 laccase by immobilization on chitosan microspheres

Laccase/mediator systems are promising bio-remediating agents as the rates of reactions can be considerably enhanced in the presence of low molecular weight mediators. A monomeric 64-kDa laccase produced by Trametes versicolor IBL-04 was effectively immobilized onto chitosan microspheres using glutaraldehyde as activating/cross-linking agent. Chitosan beads developed from 2.5% (w/v) chitosan concentration and activated by 1.5% (v/v) glutaraldehyde solution displayed best laccase immobilization efficiency. Scanning electron microscopy showed that beads with encapsulated laccase on the surface were spherical in shape having large surface area. The chitosan beads immobilized laccase (denoted as CTS -Lac) exhibited a broader active pH and temperature range and showed maximum activity at pH 6.0 and 60 degrees C. After immobilization, the affinity of the enzyme toward its substrate increased (Km decreased), leading to enhanced catalytic efficiency (Vmax increased). As compared to free laccase, the CTS -Lac showed significantly improved thermal and storage stability. The catalytic activity of the immobilized laccase was also demonstrated by the decolorization of five different textile reactive dyes. In the presence of 2,2'-azinobis-(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) as redox mediator, a maximum of 100% decolorization was achieved within the shortest time period of 4.0 h, indicating the effectiveness of CTS -Lac for the removal of textile dyes from an aqueous solution. It also retained 80.19% of its activity after ten continuous decolorization cycles for Sandal-fix Red C4BLN. The kinetic, thermo-stability and dye-decolorizing characteristics of CTS-Lac/mediator system reflect its potential for use in industrial and environmental biotechnology. (C) 2017 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.