Lignin attack during eucalypt wood decay by selected basidiomycetes: a Py-GC/MS study

Abstract

The degradation patterns of Eucalyptus globulus wood by several basidiomycetes isolated from naturally-decayed wood in eucalypt plantations in Uruguay were studied by analytical pyrolysis coupled to gas chromatography/mass spectrometry. Relative peak areas were calculated for pyrolysis products derived from guaiacylpropanoid (G) and syringylpropanoid (S) lignin units, as well as for products arising from carbohydrates. The fungal strains used were found to be efficient lignin degraders on eucalypt wood as revealed by lignin/carbohydrate ratio from pyrolysis products. Simultaneously, a decrease of lignin S/G ratio was observed during wood delignification. This is due to the preferential biodegradation of S-units, which are predominantly ether-linked, compared with G-units that are more recalcitrant towards fungal attack because of the presence of biphenyl-type structures. Both the lowest lignin/carbohydrate and S/G ratios were found in the wood treated with a Phanerochaete crassa strain. Subtle modifications of residual lignin in wood were evidenced by changes in relative abundance of pyrolysis products after fungal decay.