Depolymerization of straw lignin by manganese peroxidase from Nematoloma frowardii is accompanied by release of carbon dioxide

Manganese peroxidase preparations (MnP) from the white-rot fungus Nematoloma frowardii were able to release directly from C-14-labeled milled wheat straw (MWS; total lignin fraction) and milled straw lignin (MSL; dioxane soluble part of MWS). Apart from the formation of (CO2)-C-14, (4-10%) the treatment of insoluble MWS and MSL with MnP resulted in the formation of water-soluble C-14-lignin fragments (lignin solubilization, 14-25%). Analyses with gel permeation chromatography (GPC) demonstrated the formation of lignin fragments with predominant molecular masses around 1 kDa. The extent of MWS mineralization and solubilization was enhanced in the presence of reduced glutathione (GSH) acting as thiol mediator, whereas MSL mineralization was not stimulated by GSH. The principle of direct extracellular mineralization of lignin catalyzed by the MnP system may make a significant contribution to the formation of carbon dioxide in lignin cellulose containing habitats.