White and brown rot decay as two models for biotechnological processing of wood: Structural analysis by 2D nuclear magnetic resonance and analytical pyrolysis

Degradation of the main plant polymers was investigated after white and brown-rot fungal decay of wood under environmental conditions. The chemical changes produced in the plant cell-wall were analyzed in situ by solution nuclear magnetic resonance (NMR) at the gel state, and analytical pyrolysis. 2D-NMR of the white-rotted wood showed only cellulose and (deacetylated) hemicellulose, and the complete removal of lignin. On the other hand, the brown-rotted wood showed the nearly complete absence of polysaccharides, while the main aspects of lignin structure, as revealed by 2D-NMR, were conserved. These included well-resolved aromatic and side-chain cross-peaks, although the intensity of the latter was lowered indicating a reduction in the number of side-chain linkages (β-O-4' and resinol) per aromatic unit. These results contrast with a recent study reporting extensive ligninolysis in brown-rot decay, and concluding that the aromatic polymer remaining is not longer recognized as lignin. Here, some oxidative alteration of lignin during brown-rot decay was evidenced and, more interesting, several compounds with 3-methoxycatechol skeleton were released upon pyrolysis. Lignin demethylation is consistent with recent brown-rot transcriptomic/secretomic studies showing overexpression of methanol oxidase, which could use lignin-derived methanol to generate the peroxide required for cellulose depolymerization via Fenton chemistry.

This study was supported by the BIORENEW EU-project (NMP2-CT-2006-026456). The authors thank Aldo E. González (CBM, CSIC, Madrid) for his help in the collection and identification of the wood-rotted samples.

Peer reviewed