Efficient dye removal by Streptomyces cyaneus lacasse heterologously expressed within S. cerevisiae cell walls immobilized within tyramine-modified alginate beads using visible light photopolymerization

Abstract

Environmental pollution by synthetic dyes presents serious global problem, since they are not biodegradable in conventional anaerobic wastewater treatment. Many studies using enzymatic degradation of synthetic dyes, especially laccases were reported. For the lacasse immobilization, hydrogels obtained through UV photopolymerization have been commonly used. However, cross-linking with visible light presents a less harmful and invasive method with possible applications in tissue engineering. In this study, laccase from Streptomyces cyaneus was expressed on the surface of yeast cell walls, followed by cell lysis and immobilization within modified alginate beads. The resulting laccase biocatalysts were additionally crosslinked using visible light in the presence of riboflavin as a photoinitiator. Photopolymerization was confirmed by FTIR spectroscopy. The obtained biocatalysts with improved pH and temperature stability were obtained. At 60 ℃, cell wall-immobilized laccase entrapped in photopolymerized tyramine-alginate hydrogel showed 30% higher enzymatic activity compared to the non-photopolymerized tyramine-alginate biocatalyst, and 250% higher activity compared to the biocatalyst immobilized in native alginate beads. Photopolymerized biocatalysts were tested for the decolorization of different classes of synthetic dyes. The relative decolorization of Evans Blue and Remazol Brilliant Blue by photopolymerized biocatalysts reached 75% and 77%, respectively, without the addition of redox mediators.