Hyphal-sheath polysaccharides in fungal deterioration

The extracellular polysaccharides produced by some fungi involved in the deterioration of wood (Pleurotus species) and stone (Ulocladium atrum) were isolated and characterized. Both and β-(1 → 3)-linked glucans with considerable branching degree, as revealed by methylation analysis and 13C-NMR. The Pleurotus glucans present the most complex structure and the study was followed by the analysis of the low-molecular weight products and the partially degraded polysaccharides obtained after periodate oxidation or acetolysis. The Pleurotus species produced ligninolytic enzymes which play a role in wood deterioration. On the other hand, Ulocladium atrum produces black pigments (melanins) involved in stone biodarkening, which were studied by analytical pyrolysis and chemical degradation. The occurrence of similar extracellular polysaccharides in fungi from very different taxonomic groups, i.e. ascomycetous dematiaceous and white-rot basidiomycetes, suggests that such polysaccharides are playing some basic functions in hyphal growth on different substrates. In addition, they probably play specific roles in biodeterioration of stone, including the formation of extracellular melanin-polysaccharide stable complexes; and wood, providing a microenvironment for the action of ligninolytic enzymes and redox intermediates.