Wood biodegradation and enzyme production by Ceriporiopsis subvermispora during solid-state fermentation of Eucalyptus grandis

Abstract

The white-rot fungus Ceriporiopsis subvermispora grows on wood aggressively and is suitable for biopulping of both soft and hardwoods. This fungus is able to produce laccase and manganese peroxidase (MnP) isoenzymes, as well as hemicellulases and a poor complex of cellulases lacking in cellobiohydrolase activity. In the present work, C. subvermispora was grown on Eucalyptus grandis wood chips under solid-state fermentation. Wood weight loss ranged from 2.9 to 11.7% for biodegradation periods of 15–90 days. The highest lignin loss was 27 %, which was similar to the loss of polyoses (21.6%) after 90 days of treatment. Glucan loss started to be significant only after 60 days of biodegradation attaining a maximum of 7.3% after 90 days. Extractives removal was also significant, reaching 42% after 90 days. Holocellulose yields were almost unchanged over all the biodegradation periods. However, the holocellulose viscosities decreased as a function of the biodegradation time, especially after 30 days. The yields of alpha-cellulose decreased from 44 to 37% as a function of the biodegradation time, indicating that cellulose depolymerization took place even when the glucan losses were low. Some relevant hydrolytic and oxidative enzymes present in the culture extracts were studied. Xylanase was the main hydrolytic enzyme and the levels of peroxidase were lower than those of laccase. During the initial wood decay stages, there was not a direct correlation between the levels of enzymatic activities and the extent of losses of wood weight or components. This suggests that the mineralization of wood components might be limited by the non-diffusion of the enzymes into the wood cell walls at the initial decay stages.