LIGNIN-MODIFYING ENZYMES FROM SELECTED WHITE-ROT FUNGI - PRODUCTION AND ROLE IN LIGNIN DEGRADATION

White-rot fungi produce extracellular lignin-modifying enzymes, the best characterized of which are laccase (EC 1.10.3.2), lignin peroxidases (EC 1.11.1.7) and manganese peroxidases (EC 1.11.1.7). Lignin biodegradation studies have been carried out mostly using the white-rot fungus Phanerochaete chrysosporium which produces multiple isoenzymes of lignin peroxidase and manganese peroxidase but does not produce laccase. Many other white-rot fungi produce laccase in addition to lignin and manganese peroxidases and in varying combinations. Based on the enzyme production patterns of an array of white-rot fungi, three categories of fungi are suggested: (i) lignin-manganese peroxidase group (e.g. P. chrysosporium and Phlebia radiata), (ii) manganese peroxidase-laccase group (e.g. Dichomitus squalens and Rigidoporus lignosus), and (iii) lignin peroxidase-laccase group (e.g. Phlebia ochraceofulva and Junghuhnia separabilima). The most efficient lignin degraders, estimated by (CO2)-C-14 evolution from C-14-[Ring]-labelled synthetic lignin (DHP), belong to the first group, whereas many of the most selective lignin-degrading fungi belong to the second, although only moderate to good [C-14]DHP mineralization is obtained using fungi from this group. The lignin peroxidase-laccase fungi only poorly degrade [C-14]DHP.