Utilization of Terminalia superba Sawdust as Substrate for Laccase Production by Trametes sp. Isolate B7 under Solid State Fermentation

Abstract

Laccases catalyze a broad range of substrates due to their low substrate specificity and strong oxidative potentials. It can be produce from different sources which include plants, prokaryotes, arthropods and fungi especially Trametes sp. In this study laccases were produced by Trametes sp. isolate B7 utilizing sawdust as substrate in solid state fermentation. A fraction of the crude enzyme solution was partially purified and characterized. The highest total soluble protein (3.6 mg/mL) and laccase activity (2356 U/mL) were obtained on day 14 and 18 respectively at pH 5.0. The laccase was 2.3 and 9.0 times purified with 1487 U/mL and 5380 U/mL specific activity for pellets and dialysate respectively. The purified laccase was active in acidic pH (3.0 - 6.0) and temperature at 20 - 80°C while, stability was highest at pH 6.0 (89% for 24 hr) and 70°C (100% for 1 hr). Manganese, Lead, Mercury, Copper and Magnesium ions significantly increased laccase activity whereas Aluminium, Potassium, Iron and Zinc ions decrease activity of the purified enzyme (P = .05). EDTA activated laccase activity at 2 mM (117%) while L-cysteine inhibited enzyme activity at 1 mM - 5mM concentrations. Kinetic studies of the purified laccase showed KM 33 µM and Vmax 1.91 µMol./min/mL with molecular weight of ~36 kDa using N-PAGE. The purified laccase remained active in acidic conditions with high thermostability and resistance to inhibition of most of the metallic ions and EDTA tested. Thus, the enzyme was a versatile tool for biotechnological, industrial and bioremediation processes including polycyclic aromatic hydrocarbons, pesticides and dye wastewaters among other xenobiotics.