African Journal of Microbiology Research Vol. 6(4), pp. 779-792, 13 January, 2012 Available online at http://www.academicjournals.org/AJMR DOI: 10.5897/AJMR11.988 ISSN 1996-0808 ©2012 Academic Journals Full Length Research Paper Decolorization of textile dyes by Polyporus pseudobetulinus and extracellular laccase Pajareeya Songserm 1 , Prakitsin Sihanonth 1 , Polkit Sangvanich 2 and Aphichart Karnchanatat 3 * 1 Department of Microbiology, Faculty of Science, Chulalongkorn University, 254 Phayathai Road, Pathumwan, Bangkok 10330, Thailand. 2 Department of Chemistry, Faculty of Science, Chulalongkorn University, 254 Phayathai Road, Pathumwan, Bangkok 10330, Thailand. 3 Institute of Biotechnology and Genetic Engineering, Chulalongkorn University, 254 Phayathai Road, Pathumwan, Bangkok 10330, Thailand. Accepted 29 November, 2011 The objective of this study is to obtain new laccase and enzyme source with remarkable dye removal potential. Thirty isolates of white rot fungi were screened for extracellular laccase-production using 2,2- azinobis (3-ethylbenzothiazoline-6-sulfonate) (ABTS) assay as indicator. Among these, Polyporus pseudobetulinus strain WR77 exhibits the highest laccase activity and its suitable enzyme production medium contains; 1% (w/v) rice chaff, 0.5 g/L di-ammonium tartrate, and 0.01 g/L peptone as the carbon; inorganic and organic nitrogen sources; respectively. The laccase was 60-fold concentrated (by ammonium sulphate precipitation, Q-sepharose anion-exchange chromatography, and Superdex G-75 gel filtration chromatography) and gave the specific activity of 617.12 U/mg. The MW of prepared enzyme is 75.2 kDa under SDS-PAGE determination. Empirical analyzing results indicate that the optimum pH and temperature of the enzyme are around 40°C and pH 4, respectively. Furthermore, this enzyme can resist to wide pH range (4.0-11.0) with more than 95% maximum activity remained. The enzyme’s K m and V max , with ABTS substrate, were 447.93 M and 104.17 μmol/min/mg protein, respectively. The prepared enzyme was strongly inhibited by Hg 2+ and Fe 2+ but weakly (9.7%) stimulated by 10 mM Cu 2+ ions. The strain WR77 shows good ability in decolorizing many synthetic dyes (200 mg/L initial concentration); Ambifix Blue H3R (98% in 8 days), Ambifix Yellow H3R (24% in 10 days) and Ambifix Red HE3B (50% in 18 days). The prepared laccase alone (5 U/ml) could decolorize Ambifix Blue H3R by 65% within 15 min and Malachite Green by 80% within 24 h. It can be concluded that new enzyme and source with satisfactory dye removal potential have been successfully achieved. Further studies should be attempted to evaluate their feasibility in industrial uses. Key words: Polyporus pseudobetulinus, white-rot fungi, Laccase, dye decolorization, synthetic dyes. INTRODUCTION Lignin is a complex oxyphenyl propanoid polymer found in all vascular plants including herbaceous species where *Corresponding author. E-mail: i_am_top@hotmail.com. Tel: +662-218-8078. Fax: +662-253-3543. it provides rigidity to the wood part and takes respon- sibility in supporting and protecting the plants. Lignin polymer comprises a variety of monomers connected together by various C-C and C-O-C non-hydrolyzable bonds with an irregular arrangement of successive monomeric and inter-monomeric bonds (Dean and Eriksson, 1992), thus it can resist to hydrolytic attack. Nevertheless, it can still be degraded by various microorganisms, in particular, the white-rot fungi. These