SECRETION OF LIGNINOLYTIC ENZYMES AND MINERALIZATION OF C-14 RING-LABELED SYNTHETIC LIGNIN BY 3 PHLEBIA-TREMELLOSA STRAINS

Production of ligninolytic enzymes by three strains of the white rot fungus Phlebia tremellosa (syn. Merulius tremellosus) was studied in bioreactor cultivation under nitrogen-limiting conditions. The Mn(II) concentration of the growth medium strongly affected the secretion patterns of lignin peroxidase and laccase. Two major lignin peroxidase isoenzymes were expressed in all strains. In addition, laccase and glyoxal oxidase were purified and characterized in one strain of P. tremellosa. In contrast, manganese peroxidase was not found in fast protein liquid chromatography profiles of extracellular proteins under either low (2.4 mu M) or elevated (24 and 120 mu M) Mn(II) concentrations. However, H2O2- and Mn-dependent phenol red-oxidizing activity was detected in cultures supplemented with higher Mn (II) levels. Mineralization rates of C-14-ring-labelled synthetic lignin (i.e., dehydrogenation polymerizate) by all strains under a low basal Mn(II) level were similar to those obtained for Phanerochaete chrysosporium and Phlebia radiata. A high manganese concentration repressed the evolution of (CO2)-C-14 even when a chelating agent, sodium malonate, was included in the medium.