Demethoxylation of [O14CH3]-labelled lignin model compounds by the brown-rot fungi Gloeophyllum trabeum and Poria (Postia) placenta

Demethoxylation reactions in the cultures of the brown-rot fungi Gloeophyllum trabeum and Poria placenta were studied by determining the evolution of (CO2)-C-14 from a non-phenolic lignin model, beta-O-4 dimer, [(OCH3)-C-14]-labelled at position 4 in the A ring (model I), and from [(OCH3)-C-14]-labelled vanillic acid (model II). The fungi were grown under oxygen or air atmosphere on an agar medium with or without spruce sapwood blocks. The dimeric model (I) was impregnated onto agar or wood block in cultures to clarify the possible effect of wood as growth substrate. In the case of vanillic acid (model II), birch wood was used. The effect of supplemented nutrient nitrogen (2 mM N) and glucose (0.1 or 1.0% w/v) on demethoxylation was also studied. G. trabeum enhanced the production of (CO2)-C-14 from the dimer in the presence of spruce wood blocks. It released (CO2)-C-14 from the methoxyl groups giving 30-60% of the applied activity in 8 weeks. P. placenta produced almost 30% (CO2)-C-14 from vanillic acid (model II) in 9 weeks under oxygen, but from the methoxyl group of the dimer only 3% of (CO2)-C-14 was evolved in 4 weeks. The biomasses determined as ergosterol assay showed variation from 14 to 226 mu g g(-1) dry weight of agar, and 2 to 9 mu g g(-1)of wood, but they did not correlate with the production of (CO2)-C-14. The results indicate that these brown-rot fungi possess different mechanisms for demethoxylation.