Lignin-degrading activity and ligninolytic enzymes of different white-rot fungi: Effects of manganese and malonate

Ten species of white-rot fungi, mainly belonging to the family Polyporaceae (Basidiomycotina), were studied in terms of their ability to degrade C-14-ring labelled synthetic lignin and secrete ligninolytic enzymes in liquid cultures under varying growth conditions. Lignin mineralization by the fungi in an air atmosphere did not exceed 14% within 29 days. Different responses to the elevated Mn2+ concentration and the addition of a manganese chelator (sodium malonate) were observed among various fungal species. This could be related with the utilization of either lignin peroxidase (LiP) or manganese peroxidase (MnP) for lignin depolymerization, i.e., some fungi apparently had an LiP-dominating ligninolytic system and others an MnP-dominating ligninolytic system. The LiP isoforms were purified from Trametes gibbosa and Trametes trogii. Isoelectric focusing of purified ligninolytic enzymes revealed the expression of numerous MnP isoforms in Trametes gibbosa, Trametes hirsuta, Trametes trogii, and Abortiporus biennis grown under a high (50-fold) Mn2+ level (120 mu M) with the addition of the chelator. In addition, two to three laccase isoforms were detected.