Laccase mediated decolorization of vat dyes by Coriolus versicolor IBL-04

Five indigenous white rot fungi Pleurotus ostreatus IBL-02, Phanerochaete chrysosporium IBL-03, Coriolus versicolor IBL-04, Ganoderma lucidum IBL-05 and Schizophyllum commune IBL-06 were screened for decolorization of four vat dyes, Cibanon red 2B-MD, Cibanon golden-yellow PK-MD, Cibanon blue GFJ-MD and Indanthrene direct black RBS. The screening experiment was run for 10 days with 0.01% dye solutions prepared in alkaline Kirk's basal nutrient medium in triplicate (250 ml flasks). Every 48 h samples were read on their respective wavelengths (λmax) to determine the percent decolorization. It was observed that C. versicolor IBL-04 could effectively decolorized all the four vat dyes at varying incubation times but best results were shown on Cibanon blue GFJ-MD (90.7%) after 7 days, followed by golden-yellow (88%), Indanthrene direct black (79.7%) and Cibanon red (74%). P. chrysosporium also showed good decolorization potential on Cibanon blue (87%), followed by Cibanon golden-yellow (74.8%), Red (71%), and Indanthrene direct black (54.6%). However, rest of the strains showed poor decolorization potential on four vat dyes. C. versicolor showing maximum decolorization of Cibanon blue GFJ-MD was, therefore, selected for process optimization. The effect of varying pH, temperature, initial dye concentration and addition of carbon and nitrogen sources was investigated. Maximum decolorization (98.5%) of 0.01% Cibanon blue GFJ-MD could be achieved after 3 days at pH 5 and 30 °C temperature in the nutrient medium supplemented with 1% starch as additional carbon source. All the supplementary nitrogen sources were found inhibitory to laccase activity and dye decolorization. It was also noted that there was negligible adsorption of the dye on fungal mycelia and laccase catalyzed biodegradation was the major decolorization route.