Laccase Production By Trametes Trogii And Its Application In The Decolorization Of Synthetic Dyes

During dyeing process, dyes released from the textile, printing and dye industries pose abig threat to the environmental safety. Effluents containing dyes are highly colored, toxic andhard to be degraded; therefore, they are hazardous to the water ecosystem. Decolorization ofthese dyes by physical or chemical methods including adsorption and precipitation, chemicaldegradation or photo degradation is financially and also methodologically demanding,time-consuming and largely ineffective. Recently, decolorization of dyes through biologicalmeans, especially through fungi laccase, has gained momentums as they are economical andcan be applied to a wide range of dyes under temperate conditions.In this study, a novel fungi strain secreting laccase was isolated. Production, purificationand characterization of this laccase as well as its application for decolorizing synthetic dyeswere investigated and the results were as follows:(1) A novel laccase-secreting white-rot fungus (named SYBC-LZ) was isolated andidentified as Trametes trogii based on its ITS-5.8S rRNA gene sequence analysis andmorphological characteristics.(2) The newly isolated strain T. trogii SYBC-LZ was cultivated by three cultureprocesses i.e. solid state fermentation, submerged fermentation and static liquid fermentationto obtain an optimum method for enzyme production. Solid state fermentation was found tobe more suitable to cultivate this strain for laccase production. The culture conditions wereoptimized by “one factor at a time” method and the optimized culture medium was2.8gwoodchips and4.2g soybean cake powder mixed with13milliliter nutrition solution (Oneliter nutrition solution contains20g sucrose,25g KNO3,5g KH2PO4,3g MgSO4·7H2O,0.3gCaCl2,and0.25g CuSO4·5H2O).Under the optimized culture medium, a maximum laccaseactivity of268U/g(increased by58.6%) was obtained just within6days, which was2daysshorter than that under previous condition.(3) Laccase from T. trogii SYBC-LZ (named LAC Z) was purified from crude laccaseculture filtrate with3serial steps of ammonium sulphate precipitation, DEAE FFion-exchange chromatography and Superdex200sieve chromatography. LAC Z was found tobe a typical “blue” laccase with molecour weight of65KDa and pI of3.2, and its N-terminalamino acid sequence revealed that it was a novel T. trogii laccase.(4) The extracellular crude enzyme from T. trogii in solid substrate fermentation showedgood activity in synthetic dye color removal, decolorizing85.2%RBBR,69.6%RB4,45.6%AB129,90.2%AR1, and65.4%RB5in30min.Dye decolorizaton was carried out bylaccase in the form of crude culture filtrate, purified laccase and whole fungal cell culture andthe results showed that crude culture filtrate got more advantages concerning economical andefficiency matters. In addition, it was found that anthraquinone dyes, playing the role ofmediators, dramatically promoted the degradation of azo dyes (non-laccase substrate) whenthere was no exogenous mediator in the reaction mixture.