Effect of copper on growth and laccase production in selection of Pleurotus sajor-caju for bioremediation studies

The white-rot fungi Pleurotus sajor-caju and Herecium erinaceus were examined for their growth on malt extract agar and malt extract broth and for oxidase activity for possible use in bioremediation. Both grew well in the pH range 5 - 6 and showed enzyme activity. Pleurotus sajor-caju showed superior growth properties, particularly at pH 5 and evidence of a very active oxidase on the solid medium. Hericium erinacius had a less reactive oxidase. Oxidase activity of Pl. sajor-caju was then examined in the liquid medium supplemented with copper ion to investigate the likely presence of laccase, a copper containing oxidase enzyme. The copper had little effect on the production of biomass but stimulated the production of the enzyme by approximately 100%. Analyses, conducted in the presence of an active catalase from Aspergillus niger, were of the same order as assays in the absence of the hydrogen peroxide metabolising enzyme suggesting that the enzyme was a laccase. A possible role for Pleurotus sajor-caju and its laccase in bioremediation of heavy metals, and detoxification of environmental organic pollutants, is considered, especially where the heavy metal, copper, may be present at greater than normal biological levels