Research Article Decolorization of simulated textile dye baths by crude laccases from Trametes hirsuta and Cerrena unicolor In this study crude laccases from the white-rot fungi Cerrena unicolor and Trametes hirsuta were tested for their ability to decolorize simulated textile dye baths. The dyes used were Remazol Brilliant Blue R (RBBR) (100 mg/L), Congo Red (12.5 mg/L), Lanaset Grey (75 mg/L) and Poly R-478 (50 mg/L). The effect of redox mediators on dye decolorization by laccases was also assessed. C. unicolor laccase was able to decolorize all the dyes tested. It was especially effective towards Congo Red and RBBR with 91 and 80% of color removal in 19.5 h despite the fact that simulated textile dye baths were used. Also Poly R-478 and Lanaset Grey were partially decolorized (69 and 48%, respectively). C. unicolor laccase did not need any mediators for removing the dyes. However, T. hirsuta laccase was only able to decolorize simulated Congo Red and RBBR dye baths (91 and 45%, respectively) in 19.5 h without mediators. When using mediators the decolorization capability was enhanced substantially, e.g. Poly R-478 was decolorized by 78% in 25.5h. On the whole, both laccases showed potential to be used in industrial applications. Keywords: Cerrena unicolor / Dye decolorization / Laccase / Redox mediator / Trametes hirsuta Received: October 28, 2009; revised: January 28, 2010; accepted: February 19, 2010 DOI: 10.1002/elsc.200900095 1 Introduction In the textile industry the dyeing process results in the production of large amounts of high-colored wastewater. A special problem is found in the application of synthetic dyes since they are designed to resist fading upon exposure to sweat, light, water, many chemicals and microbial attack, which make them resistant to biodegradation [1]. In addition, many synthetic dyes are toxic, mutagenic and carcinogenic [2, 3]. Therefore, the discharge of such effluents into the water systems causes serious environmental concerns. The current techniques for the treatment of wastewater containing synthetic dyes have several drawbacks such as high cost, formation of hazardous by-products or intensive energy requirements [4]. Moreover, they fail in degrading dye mixtures. The use of bacteria in the biological treatment of synthetic dye effluents may result in the generation of colorless, dead-end aromatic amines, which are generally more toxic than the parent compounds [5]. Nowadays, environmental regulations in most countries require that wastewater must be decolorized before its discharge. This has led to the necessity of finding innovative and environmentally friendly treatment technologies to complement or substitute the conventional ones. Laccases (benzenediol:oxygen oxidoreductases; EC 1.10.3.2) are considered an appealing alternative in the development of an effective technology for the bio-treatment of textile wastewater because of their wide substrate specificity and the fact that they use molecular oxygen as a co-factor [6]. The increased interest in laccases is in part due to the finding of Bourbonnais and Paice [7] that laccases can oxidize non-phenolic compounds in the presence of redox mediators. The mechanism by which redox mediators play a role in the reactions catalyzed by laccase is now well characterized. Laccase oxidizes the redox mediator, which in turn either does a one-electron oxidation of the substrate to a radical cation or it abstracts an H-atom from the substrate converting it into a radical [8–13]. Synthetic dye decolorization research by laccases has been performed mostly with dyes dissolved into water despite the fact that the dyes are normally found in effluents that contain Ulla Moilanen 1,2 Johann F. Osma 3 Erika Winquist 1 Matti Leisola 1 Susana Rodrı ´guez Couto 3,4,5 1 Department of Biotechnology and Chemical Technology, Aalto University School of Science and Technology, Aalto, Finland 2 Department of Food and Environmental Sciences, University of Helsinki, Finland 3 Departament d’Enginyeria Quimica, Universitat Rovira i Virgili, Tarragona, Spain 4 CEIT, Unit of Environmental Engineering, San Sebastian, Spain 5 IKERBASQUE, Basque Foundation for Science, Bilbao, Spain Abbreviations: ABTS, 2,2 0 -azino-bis(3-ethylbenzthiazoline-6-sulfonate); PDA, potato dextrose agar; RBBR, Remazol Brilliant Blue R Correspondence: Ulla Moilanen (ulla.moilanen@helsinki.fi), Depart- ment of Food and Environmental Sciences, University of Helsinki, P.O. Box 27, 00014 University of Helsinki, Finland. & 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim http://www.els-journal.com 242 Eng. Life Sci. 2010, 10, No. 3, 242–247