Metabolite secretion, Fe3+-reducing activity and wood degradation by the white-rot fungus Trametes versicolor ATCC 20869

Abstract

Trametes versicolor is a promising white-rot fungus for the biological pretreatment of lignocellulosic biomass. In the present work, T. versicolor ATCC 20869 was grown on Pinus taeda wood chips under solid-state fermentation conditions to examine the wood-degrading mechanisms employed by this fungus. Samples that were subjected to fungal pretreatment for one-, two- and four-week periods were investigated. The average mass loss ranged from 5 % to 8 % (m m−1). The polysaccharides were preferentially degraded: hemicellulose and glucan losses reached 13.4 % and 6.9 % (m m−1) after four weeks of cultivation, respectively. Crude enzyme extracts were obtained and assayed using specific substrates and their enzymatic activities were measured. Xylanases were the predominant enzymes, while cellobiohydrolase activities were marginally detected. Endoglucanase activity, β-glucosidase activity, and wood glucan losses increased up to the second week of biodegradation and remained constant after that time. Although no lignin-degrading enzyme activity was detected, the lignin loss reached 7.5 % (m m−1). Soluble oxalic acid was detected in trace quantities. After the first week of biodegradation, the Fe3+-reducing activity steadily increased with time, but the activity levels were always lower than those observed in the undecayed wood. The progressive wood polymer degradation appeared related to the secretion of hydrolytic enzymes, as well as to Fe3+-reducing activity, which was restored in the cultures after the first week of biodegradation.