The application of 13C-labeled tetramethylammonium hydroxide (13C-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, 13C-TMAH thermochemolysis, to study the chemical modification of lignin by white-rot and brown-rot fungi. This technique differs from other molecular chemolysis procedures (e.g. TMAH thermochemolysis and CuO alkaline oxidation) as it enables one to determine the amount of hydroxylated aromatic components in degraded lignin residues through a selective lignin depolymerization and 13C-labeled methylation reaction. Major differences were observed in the chemical composition and yield of lignin monomers released from a limited sample set of field and laboratory inoculation brown-rot and white-rot degraded residues when analyzed by 13C-TMAH thermochemolysis. The brown-rot residues were characterized by high yields of 3,4-dihydroxy phenyl compounds, presumably due to fungal demethylation of methoxyl groups on guaiacyl lignin, and relatively low yields of aromatic acids that result from microbial side chain oxidation. The white-rot residues were characterized by low yields of demethylated lignin monomers but relatively high yields of monomers exhibiting side chain oxidation. If generally applicable, this distinct chemical functionality has important implications for the chemical reactivity and solubility of degraded wood residues and consequently the cycling of terrestrial carbon in the geosphere. The 13C-TMAH thermochemolysis procedure provides a rapid and sensitive tool for tracking microbial modifications of lignin in terrestrial environments including coastal sediments, forest soils and waters receiving terrestrial organic matter.