Manganese peroxidases, laccases and oxalic acid from the selective white-rot fungus Physisporinus rivulosus grown on spruce wood chips

The white-rot fungus Physisporinus rivulosus T241i produced manganese peroxidase (MnP), laccase, and oxalic acid when it was grown on spruce (Picea abies) wood chips. This white-rot basidiomycete degrades lignin selectively and is promising for use in biopulping of softwood. During solid-state cultivation on wood chips the fungus produced oxalic acid (28 μmol/g dry wood) and a high MnP activity (24 nkat/g dry wood), while measured laccase activity was negligible. The prepurified laccase and MnP isoforms were fractionated with anion exchange chromatography. Characterization of the isolated MnP fractions indicated the presence of several MnP isoforms with pI values between 3.4 and 3.9 and molecular masses between 47 and 52 kDa. The four laccase isoforms had pI values between 3.1 and 3.3 and molecular masses between 66 and 68 kDa. The MnP and laccase isoform profiles did not vary during the 4-week cultivation. The N-terminal amino acid sequences of four laccase and two MnP isoenzymes resembled those of the two other selective white-rot fungi applied in biopulping, i.e. Ceriporiopsis subvermispora CZ-3 and the strain IZU-154.