Biodegradation of monomeric, dimeric and polymeric lignin models by Lentinus edodes

Three monomeric, dimeric and polymeric lignin models, ferulic acid, 4-ethoxy-3-methoxyphenylglycerol- beta-2,6-dimethoxyphenyl ether, and soluble lignocellulose were incubated with Lentinus edodes ligninolitic crude extracts. Ferulic acid yielded several products of hydroxylation, demethylation and aromatic ring cleavage, and only traces of dimerization products. 4-Ethoxy-3-methoxyphenylglycerol-beta-2,6-dimethoxyphenyl ether, a beta-O-4 aryl ether lignin substructure model, yielded a cyclic carbonate, a product of both C-alpha side chain oxidation and aromatic ring cleavage as main degradation product, while only traces of products of side chain oxidative cleavage were detected. The incubation of soluble lignocellulose yielded several products of both side chain and aromatic ring cleavage. This study suggests that lignocellulose degradation by the white-rot fungus Lentinus edodes proceeds through both side chain oxidation, which yields depolymerization, and aromatic ring cleavage, which yields the complete degradation of the aromatic structures.