Enhanced formation of laccase activity by the white-rot fungus Trametes pubescens in the presence of copper

The white-rot fungus Trametes pubescens MB 89 has been identified as an out standing, although not-yet-described, producer of the industrially importan t enzyme laccase. Extracellular laccase formation could be greatly stimulat ed by the addition of Cu(II) to a simple, glucose-based culture medium. Usi ng optimum Cu concentrations (1.5-2.0 mM), maximum values for laccase activ ity of approximately 65 U/ml were obtained. The synthesis of the laccase pr otein depended on the presence of Cu in the medium as shown by Western blot analysis. Copper had to be supplemented during the exponential phase of gr owth for its maximal effect; addition during the stationary phase, during w hich laccase activity is predominantly formed, resulted in markedly reduced laccase productivity. As was shown by X-ray microanalysis of T pubescens m ycelia obtained from a laboratory fermentation, Cu was rapidly taken up by the fungal biomass. A possible explanation for this stimulatory effect of C u on laccase biosynthesis could be a role for this enzyme activity in melan in synthesis. The stimulatory effect of Cu on laccase synthesis was also ef fective for several other basidiomycetes and hence could be used as a simpl e method to boost the production of this enzyme.