Enhancing laccase production by a newly-isolated strain of Pycnoporus sanguineus with high potential for dye decolouration

Abstract

Response surface methodology (RSM) was applied to optimise laccase production by a new strain of Pycnoporus sanguineus, isolated from the Uruguayan forests, grown on bark shavings under semi-solid-state fermentation conditions. Enhancement of laccase production was studied, with a full 2⁴ factorial design with two replicates and four central points. Operating under the optimal conditions obtained (pH 3.0, yeast extract 10 g L⁻¹, glucose 5 g L⁻¹ and bark shavings 3 g), a laccase activity of nearly 3000 U L⁻¹ was achieved. Subsequently, the effect of different potential inducers on laccase production (Cu⁺², Mn⁺² and lignin) was tested using the one-factor-at-a-time approach. It was found that the addition of 0.5 mM Cu⁺² into the cultures considerably increased laccase production and, thus, maximum activity values of about 16 000 U L⁻¹ were achieved. Further, the optimised culture broth (containing mainly laccase) showed high capacity to decolourise different recalcitrant synthetic dyes such as Acid Red 88 (AR88), Reactive Black 5 (RB5) and Lanaset Grey G (LG). After selecting enzyme concentration and time of reaction, almost 70% of AR88 could be decolourised in the absence of redox mediators. However, mediators were necessary to bleach RB5 and LG. Methyl syringate was the most effective mediator for AR88 (reaching a decolouration degree over 90%) and RB5 (nearly 70%). Around 80% of LG could be decolourised in the presence of violuric acid. These promising results make this enzyme a very useful tool for developing wastewater treatments.