Juan C. González

Evaluation of toxicity and degradation of a chlorophenol mixture by the laccase produced by Trametes pubescens

In this study, the biodegradation of a mixture of 2-chlorophenol (2-CP), 2,4-dichlorophenol (2,4-DCP), 2,4,6-trichlorophenol (2,4,6-TCP) and pentachlorophenol (PCP) using the laccase produced by the white-rot fungus Trametes pubescens CBS 696.94 was evaluated. Two laccase isoenzymes with molecular weights of about 60 and 120 kDa were identified in the enzymatic crude extract. The highest laccase activity with syringaldazine was observed with pH 6.0 and 60°C, while with 2,2-azino-bis(3-ethylbenzothiazoline-6) sulphonic acid the highest activity was observed between 50 and 60°C and 3.0-4.0 pH. A biodegradation of 100%, 99%, 82.1% and 41.1% for 2-CP, 2,4-DCP, 2,4,6-TCP and PCP, respectively, was observed after 4h of reaction. The reduction in chlorophenols concentration allowed 90% reduction in mixture toxicity. In summary, these results show the feasibility of a laccase enzymatic crude extract from T. pubescens for the reduction of concentration and toxicity of chlorophenols.

Production of Trametes pubescens Laccase under Submerged and Semi-Solid Culture Conditions on Agro-Industrial Wastes

Laccases are copper-containing enzymes involved in the degradation of lignocellulosic materials and used in the treatment of phenol-containing wastewater. In this study we investigated the effect of culture conditions, i.e. submerged or semi-solid, and copper supplementation on laccase production by Trametes pubescens grown on coffee husk, soybean pod husk, or cedar sawdust. The highest specific laccase activity was achieved when the culture was conducted under submerged conditions supplemented with copper (5 mM), and using coffee husk as substrate. The crude extracts presented two laccase isoforms with molecular mass of 120 (Lac1) and 60 kDa (Lac2). Regardless of the substrate, enzymatic crude extract and purified fractions behaved similarly at different temperatures and pHs, most of them presented the maximum activity at 55 °C and a pH range between 2 and 3. In addition, they showed similar stability and electro-chemical properties. At optimal culture conditions laccase activity was 7.69±0.28 U mg-1 of protein for the crude extract, and 0.08±0.001 and 2.86±0.05 U mg-1 of protein for Lac1 and Lac2, respectively. In summary, these results show the potential of coffee husk as an important and economical growth medium to produce laccase, offering a new alternative use for this common agro-industrial byproduct.