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

Abstract

Demethoxylation reactions in the cultures of the brown-rot fungi Gloeophyllum trabeum and Poria placenta were studied by determining the evolution of (14)CO(2) from a non-phenolic lignin model, beta-O-4 dimer, [O(14)CH(3)]-labelled at position 4 in the A ring (model I), and from [O(14)CH(3)]-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 (14)CO(2) from the dimer in the presence of spruce wood blocks. It released (14)CO(2) from the methoxyl groups giving 30-60% of the applied activity in 8 weeks. P. placenta produced almost 30% (14)CO(2 )from vanillic acid (model II) in 9 weeks under oxygen, but from the methoxyl group of the dimer only 3% of (14)CO(2) was evolved in 4 weeks. The biomasses determined as ergosterol assay showed variation from 14 to 226 microg g(-1) dry weight of agar, and 2 to 9 microg g(-1 )of wood, but they did not correlate with the production of (14)CO(2). The results indicate that these brown-rot fungi possess different mechanisms for demethoxylation.

Genome, transcriptome, and secretome analysis of wood decay fungus Postia placenta supports unique mechanisms of lignocellulose conversion

“…Products of the hydrolytic attack could in turn serve as candidate substrates for copper radical oxidases and GMC oxidoreductases, thereby generating extracellular H 2 O 2 . Similarly, methanol released via demethoxylation of lignin (3,4) may play an important role in H 2 O 2 generation as a substrate for methanol oxidase. Such a role is consistent with our observed expression patterns and with previous investigations with G. trabeum (11).…”

“…This biodegradative strategy exposes the structural polysaccharides of plant cell walls, thus making them susceptible to hydrolysis by cellulases and hemicellulases. Brownrot fungi employ a different approach; although they modify lignin extensively, the products remain in situ as a polymeric residue (3,4). Given the incomplete ligninolysis that occurs during brown-rot, it remains unclear how these fungi gain access to plant cell wall polysaccharides.…”

Lignin Degradation by Fungal Pretreatment: A Review

“…Phenolic and non-phenolic de-methylation result in chemical alteration in lignin [49] which outcome of aromatic hydroxylation and ring splitting [50]. In the wood presence lignin de-methylation is operated by brown-rot [51]. Brown-rot fungi more effectively grown on herbaceous crops than woody plants [52].…”

Furfurylated wood: impact onPostia placentagene expression and oxalate crystal formation

“…Hydroxyl radical formation occurs in that location rather than near the fungal hyphae, which prevents damage to the fungus by this potent radical species (Goodell et al 2007;Arantes et al 2012). Brown-rot fungi do not metabolise lignin, but they depolymerise and modify lignin extensively and the products remain in situ as a polymeric residue (Niemenmaa et al 2007;Yelle et al 2008). Martinez et al (2009) did not find genes encoding exocellobiohydrolases and cellulose-binding domains P. placenta, but they did find an atypical brown-rot feature, i.e.…”