Trametes hirsuta and a purified laccase from this organism were able to degrade triarylmethane, indigoid, azo, and anthraquinonic dyes. Initial decolorization velocities depended on the substituents on the phenolic rings of the dyes. Immobilization of the T. hirsuta laccase on alumina enhanced the thermal stabilities of the enzyme and its tolerance against some enzyme inhibitors, such as halides, copper chelators, and dyeing additives. The laccase lost 50% of its activity at 50 mM NaCl while the 50% inhibitory concentration (IC 50 ) of the immobilized enzyme was 85 mM. Treatment of dyes with the immobilized laccase reduced their toxicities (based on the oxygen consumption rate of Pseudomonas putida) by up to 80% (anthraquinonic dyes). Textile effluents decolorized with T. hirsuta or the laccase were used for dyeing. Metabolites and/or enzyme protein strongly interacted with the dyeing process indicated by lower staining levels (K/S) values than obtained with a blank using water. However, when the effluents were decolorized with immobilized laccase, they could be used for dyeing and acceptable color differences (⌬E*) below 1.1 were measured for most dyes.It is known that 90% of reactive textile dyes entering activated sludge sewage treatment plants will pass through unchanged and will be discharged to rivers (34). Not all dyes currently used could be degraded and/or removed with physical and chemical processes, and sometimes the degradation products are more toxic (40). The traditional textile finishing industry consumes about 100 liters of water to process about 1 kg of textile materials. New closed-loop technologies such as the reuse of microbially or enzymatically treated dyeing effluents could help to reduce this enormous water consumption.Several combined anaerobic and aerobic microbial treatments have been suggested to enhance the degradation of textile dyes (5, 23, 32). However, under anaerobic conditions, azo-reductases usually cleave azo dyes into the corresponding amines, many of which are mutagenic and/or carcinogenic (10,11,32). Furthermore, azo reductases have been shown to be very specific enzymes, thus cleaving only azo bonds of selected dyes (50, 51). By contrast, laccases act oxidatively and less specifically on aromatic rings, thus having potential to degrade a wider range of compounds (43).Laccases are involved in the biodegradation of lignins, which constitute the main noncarbohydrate component in wood and are among the most abundant groups of biopolymers in the biosphere. A great number of white-rot fungi have been reported to produce the lignin-degrading enzymes laccase, lignin peroxidases, and manganese peroxidases, or at least one of these enzymes (15,16,44).Laccases (benzenediol:oxygen oxidoreductase, EC 1.10.3.2) have very broad substrate specificity with respect to the electron donor. They catalyze the removal of a hydrogen atom from the hydroxyl group of ortho-and para-substituted monoand polyphenolic substrates and from aromatic amines by one-electron abstraction to form free radicals...

Commercial azo, triarylmethane, antraquinonic, and indigoid textile dyes are efficiently decolorized with enzyme preparations from Pleurotus ostreatus, Schizophyllum commune, Neurospora crassa, Polyporus sp., Sclerotium rolfsii, Trametes villosa, and Mycelioph tora thermophila. The nature of substituents on the dyes' benzene rings influences enzyme activity, and hydroxyl and amino groups enhance decolorization. The presence of lignin peroxidase and/or manganese peroxidase in addition to laccase ( P. ostreatus, S. commune, S. rolfsii, N. crassa) increases decolorization by up to 25%. The effect of textile dyeing auxiliaries depends on the individual enzymes. Polyporus sp. and T. villosa are inhibited up to 20% by copper and iron chelating agents and anionic detergents, while the S. commune enzymes lose up to 70% of their activity.