Production of Laccase by Auerobasidium Pullulans and Cladosporium Werneckii under Optimized Conditions: Applications in Decolourization of Textile Dyes.

Abstract

Textile dye waste-water presents an enormous task in its disposal. This present study aims to identify fungus capable of producing extracellular laccases that under optimized conditions can decolourize textile dyes. Auerobasidium pullulans and Cladosporium werneckii isolated from soil and decayed wood respectively were identified as laccase producing fungi. Physiological conditions for maximal laccase production were investigated. The fungal biomass was determined to correlate laccase production and its growth. The optimized culture broth was used in decolourization of several textile dyes. A. pullulans had maximum laccase activity of 19.18 U/ml on the ninth day of incubation; it utilized glucose, maximum laccase activity was observed at 37 ˚C and pH 6.0 whereas C. werneckii preferred galactose, produced maximum activity of 1.53 U/ml on the twelfth day, had optimum activity at 30 ˚C and pH 5.0. Both fungal isolates preferred tryptophan as nitrogen source and utilized inoculum size of 24 mm and 0.3 mM of CuSO4 for optimal laccase production. A. pullulans laccase is constitutive whereas C. werneckii is inducible. The increase or decrease in laccase activity is in direct proportion to the rate of fungal growth. Optimized culture broth from A. pullulans and C. werneckii had 1.25 and 2.03 fold increase in laccase activity respectively and they were both able to decolourize malachite green specifically i. e 73% and 35% and had least decolourizing abilities on methylene blue in the absence of inducers and after three hours of incubation. The ability of these newly isolated fungal strains to produce laccase extracellularlly and also decolourize dyes would serve as a way to eliminate industrial textile waste water.