Laccase purification and characterization from Trametes trogii isolated in Tunisia: decolorization of textile dyes by the purified enzyme

A white-rot basidiomycete, isolated from decayed acacia wood (from Northwest of Tunisia) and identified as Trametes trogii, was selected in a broad plate screening because of its ability to degrade commercial dyes. In liquid cultures using a glucose–peptone medium, the sole ligninolytic activity detected was laccase. The highest laccase levels were obtained in presence of CuSO4 as inducer (around 20000 U/l). Two isoenzymes, were purified using anion-exchange and size-exclusion chromatographies. Both isoenzymes are monomeric proteins, with Mw around 62 kDa and isoelectric points of 4.3 and 4.5, showing similar stability at pH and temperature, optimum pH and substrate specificity. The highest oxidation rate was obtained at pH 2 and 2.5 for ABTS and DMP, respectively. They were stable up to 50 °C for 24 h and the stability was higher at alkaline pH. Activity increased by the addition of 10 mM Ni, Mo or Mn but it was not affected by Cd, Al, Li and Ca. Identical N-terminal sequences were determined in both laccases. The crude enzyme, as well as the purified laccase, was able to decolorize dyes from the textile industry.