Ligninolytic system formation by Phanerochaete chrysosporium in air

Abstract

This study characterizes the effect of oxygen concentration on the synthesis of ligninolytic enzymes by Phanerochaete chrysosporium immobilized on polyurethane foam cubes in a nonimmersed liquid culture system and maintained under different carbon-to-nitrogen (C/N) ratios and levels. Lignin peroxidase (LIP) activity was obtained in cultures exposed to air when the C/N ratio was low (7.47), i.e., when nitrogen levels were high (C/N = 56/45 mM) or carbon levels were low (C/N = 5.6/4.5 mM). At the low C/N ratio, the fungus was carbon starved and did not produce extracellular polysaccharides. At a high C/N ratio (153), i.e., under conditions of excess carbon (nitrogen limitation) (C/N = 56/2.2 mM), cultures exposed to air produced large amounts of polysaccharide, and LIP activity was detected only in cultures exposed to pure oxygen. Under high-nitrogen conditions, LIP production was 1,800 U/liter in cultures exposed to pure oxygen and 1,300 U/liter in cultures exposed to air, with H1 and H2 being the main isoenzymes. The oxygen level did not significantly alter the isoenzyme profile, nor did low-carbon conditions. The formation of manganese peroxidase was generally less affected by the oxygen level than that of LIP but was considerably reduced by a low C/N ratio. The effects of oxygen level and C/N ratio an the synthesis of glyoxal oxidase paralleled their effects on LIP synthesis except in the case of high nitrogen, which totally suppressed glyoxal oxidase activity.