Lignin degradation by a white-rot fungus lacking lignin peroxidase and manganese peroxidase

Phanerochaete chrysosporium has been the organism of choice for studies of lignin degradation and much of this work has focused on two phenol oxidases, lignin peroxidase (LiP) and manganese peroxidase (MnP), secreted by the fungus under ligninolytic conditions. However, many white-rot fungi, including a number of aggressive lignin degraders, seem to operate without expressing LiP activity. Laccase is another phenol oxidase that white-rot fungi often produce. However, the role played by laccase in lignin degradation has remained obscured since its low redox potential appeared to make it incapable of oxidizing non-phenolic lignin constituents. We have identified, Pychnoporus cinnabarinus lacking both LiP and MnP, but a high producer of laccase, to degrade lignin as efficiently as UP producing fungi. We have found that P. cinnabarinus, to overcome the redox potential barrier for laccase, produces a mediator for oxidation of non-phenolic lignin structures. This is the first description of how laccase may be used in a biological system for the degradation of lignin.