Role of Pycnoporus coccineus laccase in the degradation of aromatic compounds in olive oil mill wastewater

In a previous work was reported the ability of Pycnoporus coccineus to decolorize olive oil mill wastewaters (OOMW) without an additional carbon source. We studied the composition of the enzymatic system involved in the process. The fungus secreted only laccase under the different culture conditions studied even in presence of compounds promoting the production of peroxidases. The highest laccase levels were attained in Cu2+-ethanol medium (100,000 U/l after 45 incubation-days). A single isoenzyme was purified with a yield of 79%. This laccase is a glycoprotein (8% N-linked carbohydrate) with a molecular mass and pI of 61.5 kDa and 3.7, respectively. The highest oxidation rate was obtained around pH 3.5 for ABTS and DMP and the highest DMP oxidation at 60 °C. The enzyme was stable at pH 7 at room temperature and showed a half-life of 8 and 2 h at 50 and 60 °C, respectively. The treatment of OOMW with the laccase showed similar results to those reported with the fungus indicating that laccase plays an important role in the degradative process. The high levels of laccase secreted by P. coccineus and its stability suggest that it could be a useful tool for this and other environmental applications.