Production of ligninolytic enzymes and synthetic lignin mineralization by the bird's nest fungus Cyathus stercoreus

Production of ligninolytic enzymes and degradation of C-14-ring labeled syn thetic lignin by the white-rot fungus Cyathus stercoreus ATCC 36910 were de termined under a variety of conditions. The highest mineralization rate for C-14 dehydrogenative polymerizates (DHP; 38% (CO2)-C-14 after 30 days) occ urred with 1 mM ammonium tartrate as nitrogen source and 1% glucose as addi tional carbon source, but levels of extracellular laccase and manganese per oxidase (MnP) were low. In contrast, 10 mM ammonium tartrate with 1% glucos e gave low mineralization rates (10% (CO2)-C-14 after 30 days) but higher l evels of laccase and manganese peroxidase. Lignin peroxidase was not produc ed by C. stercoreus under any of the studied conditions. Mn(II) at 11 ppm g ave a higher rate of C-14 DHP mineralization than 0.3 or 40 ppm, but the hi ghest manganese peroxidase level was obtained with Mn(II) at 40 ppm. Cultiv ation in aerated static flasks gave rise to higher levels of both laccase a nd manganese peroxidase compared to the levels in shake cultures. 3,4-Dimet hoxycinnamic acid at 500 mu M concentration was the most effective inducer of laccase of those tested. The purified laccase was a monomeric glycoprote in having an apparent molecular mass of 70 kDa, as determined by calibrated gel filtration chromatography. The pH optimum and isoelectric point of the purified laccase were 4.8 and 3.5, respectively. The N-terminal amino acid sequence of C. stercoreus laccase showed close homology to the N-terminal sequences determined from other basidiomycete laccases. Information on C. s tercoreus, whose habitat and physiological requirements for lignin degradat ion differ from many other white-rot fungi, expands the possibilities for i ndustrial application of biological systems for lignin degradation and remo val in biopulping and biobleaching processes.