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. (C) 2013 Society of Chemical Industry