Effect of an extracellular laccase ofRigidoporus lignosus onHevea brasiliensis lignin

The abilities of white-rotting fungi to depolymerize lignin and to excrete laccases (p-diphenoloxidases), though brown-rotting fungi do not present these two biological properties, are the main differences between these two types of rotting fungi. Therefore it was assumed that the lignin scission was a result of the laccase reaction. Nevertheless,in vivo, this enzyme may play other major roles such as detoxifying of the medium by oxidation or condensing fungal growth-inhibiting phenolics. AsR. lignosus (causing a white rot on Hevea roots) secretes two laccases, our purpose was to determine whether these enzymes are able to depolymerize the lignin macromolecule or not. This was realized by showing the effect of theR. lignosus purified laccase L1 on the lignin polymerization degree by using Sephadex G100, G50, or G25 gel filtration.