Production and Optimization of Laccase by Trametes sp. Isolate B7 and Its’ Dye Decolourization Potential

Abstract

Laccases produced by Trametes sp. are extracellular multi-copper oxidases, capable of oxidising large number of xenobiotics including dyes. Challenges often encountered in large-scale utilisation include the high cost of production, low yield and unstable enzymes. Lignocellulosics which abound locally are suitable low-cost alternative substrates for laccase production in Solid State Fermentation. Trametes sp. isolate B7 (GenBank accession number MK024175) was isolated and identified using molecular techniques. The study optimised laccase production using saw-dust of Terminalia superba as well as the application of same for dye decolourisation. Optimal pH and temperature were 5.0 (2356 U/mL) and 25°C (2395 U/mL) respectively. Cu2+, Ca2+, Mn2+ and ammonium chloride induced high laccase production at 1-2 mM (2379 U/mL), 3-4 mM (2385 U/mL), 60 mM (2026 U/mL) and 0.3 g/L (2024 U/mL) respectively. Optimum incubation time, carbon source and inducer were day 18 (2395 U/mL), glucose (2395 U/mL) and 2,2’-azinobis(3-ethylbenzthiazole-6-sulphonate (ABTS) respectively. The purified laccase had a specific activity of 5830 U/mL and a molecular mass of ~36 kDa using N-PAGE. Dye decolourisation potential of the crude enzyme was RBBR 100% (24 hours), Phenol red 28% (48 hours) while Congo red, Malachite green and Crystal violet were 75%, 62% and 40% respectively after 72 hours. The ability of the crude laccase to oxidise Phenol red and other dyes without the use of mediators is an unusual character and makes it a versatile biotechnological tool for many industrial processes including bioremediation of dyes with resultant eco-friendly benefits.