Characterization of trembling aspen wood (Populus tremuloides L.) degraded with the white rot fungus Ceriporiopsis subvermispora and MWLs isolated thereof

Trembling aspen wood (Populus tremuloides L.) was treated with white rot fungus Ceriporiopsis subvermispora for 1, 2, 4, and 6 weeks. As fungal decay advanced, lignin contents were decreased gradually up to ca. 27.5% (based on the Klason residues of the control) after 6 weeks. Alkali solubility of cell wall residues was increased until 4 weeks of fungal treatment, but additional treatment did not cause any effects. Milled wood lignins (MWLs) were isolated from the decayed woods by Bjorkman's procedure and subjected to thioacidolysis and analytical pyrolysis to investigate the modification of lignin structures during fungal degradation. Thioacidolysis revealed that the yields of trithioethylated C6C3 monomers, as a parameter for frequency of beta-O-4 linkages in lignin, were substantially reduced (-20%, based on the control) in MWLs isolated from decayed woods. Analytical pyrolysis revealed that the relative amounts of coniferyl alcohol and sinapyl alcohol in the pyrolysates were lowered dependent on the biodegradation time, whereas an elevation of C6C1 and C6C2 pyrolytic phenols was observed. The results from both analytical methods strongly suggested that beta-O-4 linkages were cleaved by C. subvermispora. Specially, degradation of syringyl-type lignin seems to be preferred.