Laccase production optimization by response surface methodology with Aspergillus fumigatus AF1 in unique inexpensive medium and decolorization of different dyes with the crude enzyme or fungal pellets.

In the present study, alkaline pretreatment was applied for the enhanced laccase production from rice straw. Various process parameters including sodium hydroxide concentration, pH and fermentation temperature were optimized via response surface methodology (RSM) with a Box-Behnken design (BBD). Through regression analysis, it was found that laccase activity was well fitted by a quadratic polynomial equation (R(2)=0.998, Adj R(2)=0.995), and the fermentation temperature was the most significant factor influencing laccase activity. The optimized process conditions found were NaOH concentration of 0.39 mol L(-1), pH 3.12 and temperature 25.43 °C, under which laccase activity reached 142,198 ± 3586 U L(-1). Further studies were carried out to probe different dyes decolorization ability of laccase produced by Aspergillus fumigatus, A. fumigatus pellets and whole fermentation broth (WFB) using sodium hydroxide pretreated rice straw as sole carbon source. Results showed that pure laccase demonstrate limited decolorization ability to all the studied dyes, while crude laccase, A. fumigatus pellets and WFB exhibit significant decolorization ability to all the studied dyes with WFB being the most excellent one. Effectiveness of degradation was confirmed by uv-vis and phytotoxicity studies, which indicated that A. fumigatus transformed the dyes into non-toxic metabolites.