The effect of culture conditions on the production of lignin modifying enzymes by the white-rot fungus Phlebia radiata

Abstract

The extracellular enzymes synthesized by Phlebia radiata Fr. 79 (ATCC 64658) under various cultivation conditions were studied in order to find out suitable enzyme combinations for the modification of lignin. The fungus produced lignin peroxidase (LiP, ligninase), manganese-dependent peroxidase (MnP) and laccase (benzenediol: oxygen oxidoreductase, EC 1.10.3.2) in various proportions depending on the cultivation conditions. Addition of veratryl alcohol increased lignin peroxidase and manganese-dependent peroxidase activities both in agitated and non-agitated flask cultures. Laccase production was more enhanced by the addition of benzyl alcohol and veratric acid. However, the highest lignin peroxidase activities were obtained using a non-phenolic dimeric β- O-4 model compound. Pressure ground wood (PGW), chemithermomechanical pulp (CTMP) or spruce shavings in the bioreactors decreased the amount of lignin peroxidase, whereas laccase and manganese-dependent peroxidase activities increased. Lignin peroxidase and partly manganese-dependent peroxidase was adsorbed on the lignocellulose substrate, but laccase remained in the culture liquid. Here the lignin peroxidase activity was due to isozyme LiP3. In flask cultures more lignin peroxidase isozymes were secreted, the major component of which was the isozyme LiP2.