OVERPRODUCTION OF LIGNIN PEROXIDASE BY PHANEROCHAETE-CHRYSOSPORIUM (BKM-F-1767) UNDER NONLIMITING NUTRIENT CONDITIONS

The ligninolytic enzymes synthesized by Phanerochaete chrysosporium BK M-F-1767 immobilized on polyurethane foam were characterized under lim iting, sufficient, and excess nutrient conditions. The fungus was grow n in a nonimmersed liquid culture system under conditions close to tho se occurring in nature, with nitrogen concentrations ranging from 2.4 to 60 mM. This nonimmersed liquid culture system consisted of fungal m ycelium immobilized on porous pieces of polyurethane foam saturated wi th liquid medium and highly exposed to gaseous oxygen. Lignin peroxida se (LIP) activity decreased to almost undetectable levels as the initi al NH4+ levels were increased over the range from 2.4 to 14 mM and the n increased with additional increases in initial NH4+ concentration. A t 45 mM NH4+, LIP was overproduced, reaching levels of 800 U/liter. In addition, almost simultaneous secretion of LIP and secretion of manga nese-dependent lignin peroxidase were observed on the third day of inc ubation. Manganese-dependent lignin peroxidase activity was maximal un der nitrogen limitation conditions (2.4 mM NH4+) and then decreased to 40 to 50% of the maximal level in the presence of sufficient or exces s initial NH4+ concentrations. Overproduction of LIP in the presence o f a sufficient nitrogen level (24 mM NH4+) and excess nitrogen levels (45 to 60 mM NH4+) seemed to occur as a response to carbon starvation after rapid glucose depletion. The NH4+ in the extracellular fluid rea ppeared as soon as glucose was depleted, and an almost complete loss o f CO2 was observed, suggesting that an alternative energy source was g enerated by self-proteolysis of cell proteins. The peak level of CO2 c oncentration in the cultures increased with increasing NH4+ concentrat ions, reaching an almost asymptotic value at 24 mM NH4+ and parallelin g glucose consumption. Sodium dodecyl sulfate-polyacrylamide gel elect rophoresis and anion-exchange high-performance liquid chromatography a nalyses of heme protein composition in the extracellular fluid reveale d that LIP synthesis in the presence of sufficient and even excess nit rogen concentrations was characterized not only by increasing activity but also by isoenzyme distribution. The H2 heme protein was the predo minant LIP isoenzyme (around 70% of the total heme content) under nonl imiting conditions, in contrast to the substantial levels of all of th e ligninolytic isoenzymes under N-limiting conditions.