The application of C-13-labeled tetramethylammonium hydroxide (C-13-TMAH) thermochemolysis to the study of fungal degradation of wood

This paper presents the results from an assessment of the application of a new molecular analytical procedure, C-13-TMAH thermochemolysis, to study th e chemical modification of lignin by white-rot and brown-rot fungi. This te chnique differs from other molecular chemolysis procedures (e.g, TMAH therm ochemolysis and CuO alkaline oxidation) as it enables one to determine the amount of hydroxylated aromatic components in degraded lignin residues thro ugh a selective lignin depolymerization and C-13-labeled methylation reacti on. Major differences were observed in the chemical composition and yield o f lignin monomers released from a limited sample set of field and laborator y inoculation brown-rot and white-rot degraded residues when analyzed by C- 13-TMAH thermochemolysis. The brown-rot residues were characterized by high yields of 3,4-dihydroxy phenyl compounds, presumably due to fungal demethy lation of methoxyl groups on guaiacyl lignin, and relatively low yields of aromatic acids that result from microbial side chain oxidation. The white-r ot residues were characterized by low yields of demethylated lignin monomer s but relatively high yields of monomers exhibiting side chain oxidation. I f generally applicable, this distinct chemical functionality has important implications for the chemical reactivity and solubility of degraded wood re sidues and consequently the cycling of terrestrial carbon in the geosphere. The C-13-TMAH thermochemolysis procedure provides a rapid and sensitive to ol for tracking microbial modifications of lignin in terrestrial environmen ts including coastal sediments, forest soils and waters receiving terrestri al organic matter. (C) 2000 Elsevier Science Ltd. All rights reserved.