Directional degradation of lignocellulose by Phlebia radiata

The white-rot fungus Phlebia radiata preferably degrades lignin and is thus a potential fungus for biopulping and other applications in the pulp and paper industry. To elucidate important factors involved in the degradation of lignin carbohydrate complex (LCC) by this fungus, the metabolism of [U- ¹⁴C]-labelled wheat straw, [¹⁴C]-labelled cellulose and [¹⁴C]-labelled wheat straw hemicellulose was studied. The degradation of hemicellulose and lignin were apparently linked together and controlled by some common factors (e.g. oxygen, the effect of supplemented aromatic compounds) whereas the degradation of cellulose usually occurred under different conditions. In most cases the amount of nutrient nitrogen did not influence the evolution of ¹⁴CO, from carbohydrates. Addition of a small amount of glucose (0.05%, 2.8 mM) strongly decreased the degradation of cellulose but enhanced lignin degradation. Under oxygen atmosphere the degradation of hemicellulose was not influenced by added glucose (low nutrient nitrogen), which implied that low amounts of glucose could be used to specifically promote lignin degradation by P. radiata. The accelerating effect was most prominent under 100% oxygen atmosphere. Aromatic compounds strongly repressed the degradation of cellulose. In contrast, the degradation of hemicellulose was not influenced by aromatic compounds in air but under 100% oxygen the fungus degraded 35-70% more hemicellulose (to ¹⁴CO₂) when aromatic compounds were present than without them. The degradation of lignin was either stimulated or repressed by aromatic compounds, depending on the type of the compound used.