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

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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°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.

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