Biological Delignification of Aspen Wood by Solid-State Fermentation with the White-Rot Fungus Merulius tremellosus

Abstract

Solid-state fermentation of aspen (Populus tremuloides) wood with Merulius tremellosus for 8 weeks removed 52% of the lignin but only 12% of the total wood weight, and increased the cellulase digestibility to 53% from 18%. Water-soluble and enzyme-solubilized lignin degradation products accumulated. Delignification was fastest at temperatures between 25 and 32.5 degrees C and at a water-to-wood ratio of 2. Initial pH values between 4 and 6 were optimal; M. tremellosus acidified the wood to below pH 3.5 as it grew. The fungus tolerated CO(2) concentrations of at least 14% and O(2) concentrations down to 7% in the bulk gas phase. Both simple and complex nitrogen supplements inhibited delignification. Supplementary KH(2)PO(4), MgSO(4), CaCl(2), thiamine, and trace elements had little effect on the fermentation. Four isolates of M. tremellosus had very similar abilities to delignify aspen wood. Biological delignification with M. tremellosus may be a useful pretreatment for enzymatic saccharification or ruminant feeding.