BIODEGRADATION MECHANISM OF LIGNIN BY WHITE-ROT BASIDIOMYCETES

White-rot basidiomycetes such as Coriolus versicolor, Phanerochaete chrysosporium and Phlebia radiata have been found as typical lignin degrader. During the past 15 years chemistry and biochemistry of lignin biodegradation by white-rot basidiomycetes have considerably advanced by means of chemical analysis of the biodegraded lignin and studies of the degradation mechanism of lignin substructure model compounds by ligninolytic cultures of these basidiomycetes and their enzymes. Excellent reviews (Kirk and Farrell, 1987; Schoemaker, 1990; Umezawa and Higuchi, 1991) concerning microbial and enzymatic degradation of lignin have recently appeared. We (Higuchi and Nakatsubo, 1980; Higuchi, 1990) synthesized major lignin substructure model compounds linked by beta-O-4, beta-5, beta-1, beta-beta' and 5-5' bonds and used as substrates for cultures of P. chrysosporium and C. versicolor and their enzymes, lignin peroxidase and laccase. The degradation products were extracted with ethyl acetate and identified by NMR and GC-MS to elucidate degradation pathways of the lignin substructure model compounds. The results are classified to the cleavage of side chain and aromatic ring opening of the compounds.