DEGRADATION OF LIGNIN-CARBOHYDRATE COMPLE X (LCC) BY WOOD-ROTTING FUNGI .2. STRUCTURAL-ANALYSIS OF DEGRADED LIGNIN-CARBOHYDRATE COMPLEX

Two wood-rotting fungi, Tyromyces palustris (Berk. and Curt.) Murr. an d Coriolus versicolor (L.: Fr.) Quel, were incubated for 31 days in a medium containing a water-soluble lignin-carbohydrate complex (LCC) as a sole carbon source, and the chemical structure of the Fraction P-1 formed as an insoluble material during the incubation was characterize d. Although the neutral sugar compositions of the Fraction P-1 from bo th fungi did not show characteristic changes during the incubation, re markable differences were found in the lignin portion. In the case of T. palustris, results of functional and spectral analyses indicated th e occurrence of a slight modification of the lignin portion, and the m olecular weight of the Fraction P-1 decreased from about 4,000 to 2,90 0. On the other hand, an attack on the lignin portion by C. versicolor was found to occur in at least two steps. The first was initiated aft er about 7 days of incubation. In this step, the contents of phenolic hydroxyl and alpha-carbonyl groups decreased, whereas an increase of c arboxylic acid and an increase in molecular weight from 3,600 to 6,400 were observed, indicating the occurrence of a side-chain modification and the polymerization of lignin. The second step was initiated after about 21 days of incubation. At this step, an increase in the phenoli c hydroxyl group content was noticed, and carbon -13 nuclear magnetic resonance (C-13- NMR) spectroscopic and gel-permeation chromatographic (GPC) analyses indicate the occurrence of cleavage of the aryl-ether linkages of lignin, leading to the decrease in its molecular weight. I n addition, bondings between lignin and hemicellulose were cleaved acc ompanied by depolymerization of LCC in the case of C. versicolor.