Gary F. Leatham

Assessment of 30 White Rot Basidiomycetes for Selective Lignin Degradation

Thirty wood-inhabiting basidiomycetes were screened for their ability to selectively delignify wood, The amount of lignin and carbohydrates removed and the mo hological and ultrastructural characteristics of the decayed wood were the major criteria used to determine fungi with superior lignin-degrading ability. Phellinus pini-2, Pholiota mutabilis, Phlebia brevispora-l and Phanerochaete chrysosporium were the best delignifiers of both birch and pine. Different isolates of the same species of fungi differed in both the type of decay caused and their selectivity for lignin. Almost all fungi tested caused greater weight losses in birch blocks than in pine blocks. Most fungi isolated from gymnosperms caused greater weight losses in pine than did isolates from angiosperms. The fungi studied produced two different types ofselective delignification. The first type resulted in extensive lignin removal from localized areas within wood blocks. The second type resulted in a more uniform loss throughout wood blocks, but less extensive loss from individual cell walls.

Selection of white-rot fungi for biopulping☆

Abstract Different rates of wood decay and ligninolytic activity were found in wood decayed by various white-rot fungi. Chemical and ultrastructural analyses showed wood decayed by Coriolus versicolor consisted of a nonselective attack on all cell wall components. Lignin degradation was restricted to the cell wall adjacent to hyphae or around the circumference of cell lumina. Decay by Phellinus pini, Phlebia tremellosus, Poria medullapanis and Scytinostroma galactinum was selective for lignin degradation. Secondary walls were void of lignin and middle lamellae were extensively degraded. A diffuse attack on lignin occurred throughout all cell wall layers. Variation in ligninolytic activity was found among strains of Phanerochaete chrysosporium . Differences in weight loss as well as lignin and polysaccharide degradation were also found when wood of different coniferous and deciduous tree species was decayed by various white-rot fungi.

Lignin distribution in wood delignified by white-rot fungi: X-ray microanalysis of decayed wood treated with bromine

Lignin concentration was determined in cell wall layers of sound and white-rotted birch and pine wood using energy dispersive X-ray analysis. Two types of selective lignin removal were identified. In one type, characteristic of Phellinus pini decay, lignin was completely removed from all cell wall layers, but only in localized areas of wood blocks. In the other type, characteristic of Pholiota mutabilis and Phanerochaete chrysosporium decay, extensive amounts of lignin were uniformly removed from wood blocks, but the major attack occurred in the S2 layer of fiber cell walls with virtually no degradation of cell corners. Phlebia subserialis, a non-selective lignin degrading fungus, removed similar amounts of lignin from wood blocks äs Phell. pini and PhoL mutabilis, but complete dissolution of all cell wall components occurred where lignin was degraded. The process of lignin removal from wood cell walls, whether selective or not, varies among white rot basidiomycetes.