Structural Characterization of Lignin during Pinus taeda Wood Treatment with Ceriporiopsis subvermispora

Abstract

Although lignin is recalcitrant, some specialized fungi developed the ability to degrade this complex molecule. Most of these fungi belong to the basidiomycetes and are responsible for the white-rot decay process (19). White-rot fungi use an intricate oxidative complex to degrade lignin, which is based on oxidative enzymes and low-molecular-mass mediators (28). Several white-rot fungi produce a lignin peroxidase (LiP) that can initiate one-electron oxidation of nonphenolic arylglycerol-␤-O-aryl ether units. This oxidation is followed by C␣-C␤ or ␤-O-aryl cleavage to give aromatic aldehydes or phenylglycerols, respectively, as primary products (19). On the other hand, some white-rot fungi degrade lignin efficiently without producing LiP (20). One of them, Ceriporiopsis subvermispora, has been extensively studied (15,16,17,31,32), owing to its suitability for biopulping (1,27). Although the industrial applicability of this fungus has been recognized, its ligninolytic strategies are not completely understood. It has often been assumed that lignin degradation by C. subvermispora is dependent on manganese-dependent peroxidases and laccases (28). The occurrence of lignin degradation inside the wood matrix during the first stages of wood decay, when low cell wall permeability does not permit enzyme diffusion, has clearly indicated that some low-molecular-mass agents also act in the early stages of lignin biodegradation (2). Lipid peroxidation induced by manganese-dependent peroxidase has been proposed for lignin biodegradation by C. subvermispora (6,17,18,32). Studies with lignin model compounds have shown that nonphenolic arylglycerol-␤-O-aryl units are disrupted by means of one-electron oxidation mechanisms similar to the routes proposed for basidiomycetes that produce LiP (18,32).Under solid-state fermentation of wood, C. subvermispora extensively depolymerizes lignin. Lignin depolymerization has been demonstrated in studies based on the molecular mass distribution of milled wood lignins (MWLs) recovered from biotreated wood samples (15) and in studies using in situ derivatization followed by reductive cleavage (DFRC) of lignin in biotreated wood, which indicates lignin depolymerization as a consequence of aryl-ether degradation (16).The present study provides additional data for evaluating lignin biodegradation by C. subvermispora during solid-state fermentation of Pinus taeda wood. The structural characteristics of MWLs extracted from sound (untreated) and biotreated wood samples were elucidated using wet-chemical and spectroscopic analyses. MATERIALS AND METHODSFungus, inoculum preparation, and wood biodegradation. C. subvermispora (Pilat) Gilbertson et Ryvarden cultures were maintained on 2% (wt/vol) malt extract agar plates at 4°C. The wood chips (approximately 2.5 by 1.2 by 0.2 cm) used in this work came from a single log of a 28-year-old P. taeda tree.Biodegradation experiments were carried out in 20-liter polypropylene bioreactors. Precolonized wood chips were used as inoculum seed to start the colonization ...

A Highly Diastereoselective Oxidant Contributes to Ligninolysis by the White Rot Basidiomycete Ceriporiopsis subvermispora

“…2). Benzoic acids were found previously in lignin degraded by P. chrysosporium (12, 13) but were not reported in an analysis of lignin degraded by C. subvermispora (24). Therefore, we performed an additional 1 H-13 C HMBC experiment after acetylation of the C. subvermispora and control samples.…”

“…To complicate the picture further, although previous work with lignin model compounds suggested that C. subvermispora cleaves lignin between C ␣ and C ␤ , consistent with the operation of a SET oxidant (23), a later analysis of wood degraded by the fungus did not reveal C ␣ OC ␤ cleavage products in the residual lignin (24). Thus, not only the nature of the ligninolytic oxidants but also the chemical route for ligninolysis remains in question for this biotechnologically promising fungus.…”

Effects of Two-Stage Dilute Acid Pretreatment on the Structure and Composition of Lignin and Cellulose in Loblolly Pine

“…Isolation and characterization of milled wood lignin Milled wood lignin was extracted from the starting biomass and pretreated wood according to the method outlined by Guerra et al [45] and Holtman et al [46]. The Loblolly pine woodchips was milled using a Wiley mill to pass through a 0.50 mm screen and 50 g ground wood was treated with 1:2 (v/v) ethanol: benzene for 24 h in a Soxhlet apparatus followed by a 24 h Soxhlet treatment with ethanol to remove extractives.…”

Changes in chemical composition of decayed Scots pine and beech wood

“…Likewise, Fourier transform infrared (FT-IR) analysis on decayed wood by brownrot fungi [3,[5][6][7][21][22][23], white-rot fungi [10,[24][25][26][27], both brown and white-rot fungi [8,20,[28][29][30], and soft-rot fungi [31,32] were extensively studied. Because outdoor conditions influence service life of wood in many applications, studying effect of both biological agents and environmental conditions on wood properties is gaining an importance.…”