Copper-binding proteins in ectomycorrhizal fungi

The presence of copper-binding proteins produced in response to added copper was examined in isolates of Laccaria laccata (Scop. ex Fr.) Cooke and Paxillus involutus (Batsch ex Fr.) Fr. taken from copper-contaminated and uncontaminated sites, and in a single isolate of Scleroderma citrinum Pers. from a contaminated site. Two isolates of Laccaria (GLac4 and ELac1) grew better in 1.5 mM and 2.5 mM copper than a third (Lac3G) and were considered to be more tolerant. Amongst five isolates of P. involutus, three (WJPax2R, GPaxRSp2 and Pax4) were capable of growth in media containing 4.0 mM copper and were regarded as tolerant. All isolates of both Laccaria and Paxillus were capable of some growth in 2.5 mM copper, but S. citrinum was much more copper-sensitive and the concentration had to be reduced at least 10-fold before any growth occurred. Tolerance of isolates was not related to whether they were taken from copper-contaminated or uncontaminated sites. Copper-binding proteins were detected in response to copper in the culture media in the two tolerant isolates of Laccaria (GLac4 and ELac1) but not in the least tolerant isolate. In Paxillus, similar proteins were found in two tolerant isolates (GPaxRSp2 and Pax4) but not in WJPax2R, which was also regarded as tolerant, nor in any of the less tolerant isolates. Copper-binding proteins were not detected in S. citrinum. The copper-binding protein purified from the Laccaria isolate ELac1 appeared as a single band in modified SDS-PAGE electrophoresis. Its molecular mass and spectral characteristics were consistent with it being a metallothionein.