Characterization of yellow bacterial laccase SmLac/role of redox mediators in azo dye decolorization

BACKGROUND The bacterial Stenotrophomonas maltophilia AAP56 laccase ( SmLac ) has been purified from cell extracts and its spectral and kinetic properties studied. It shows a high decolorization rate (99%) of the diazoic dye Reactive Black 5 ( RB5 ) in the presence of redox mediators such as ABTS (2,2′‐azino‐bis(3‐ethylbenzthiazoline‐6‐sulfonic acid), ASGN (Acetosyringone), SGA (Syringaldehyde) and HOBT (1‐Hydroxy‐Benzotriazole). The optimal pH has been determined as neutral or basic compatible with textile wastewater pH for further treatment application. RESULTS This paper reports the characterization of the catalytic center of purified SmLac as not a classic blue laccase but a yellow one. Its redox potential has been determined at 638 mV , which indicates that the enzyme is a versatile laccase able to oxidase a wide range of substrates. Performance of the enzyme as catalyst for RB5 decolorization in association with a redox mediator has been demonstrated to be a promising bioremediation process since it presents high degradation ability (almost 99% in 1 h reaction time). The study also demonstrated, by electrochemical studies of redox potential of both mediators/protein and following the driving electron force, the importance of the choice of redox mediator and the limiting step in the laccase mediated reaction in azo dye decolorization. CONCLUSION It was demonstrated that the bacterial laccase SmLac has great potential for biotechnological applications (such as azo dye decolorization) compared with Trametes versicolor laccase.