Lignin is a long chain heterogeneous polymer composed largely of phenylpropane units most commonly linked by ether bonds. It effectively protects the woody plants against microbial attack and only a few organisms including rot-fungi and some bacteria can degrade it (57). The conversion of cellulose and hemicellulose to fuels and chemicals will generate lignin as a by-product that can be burned to provide heat and electricity, converted to low-molecular weight chemicals, and used in the manufacture of various polymeric materials. As lignin makes up 15-25% in some lignocellulosic biomass, the selling price of lignin has a very large impact on ethanol price (18).

In recent years, removal of lignin from lignin-carbohydrate complex (LCC) has received much attention because of potential application in pulp and paper industry. The lignin barrier can be disrupted by a variety of pretreatments rendering the cellulose and hemicellulose more susceptible to enzymatic attack (52). There are many papers about microbial breakdowns of lignin, the enzymes and the pathways (55-56). The degradation of lignin by the basidiomycete Phanerochaete chrysosporium is catalyzed by extracellular peroxidases (lignin peroxidase, Lip and manganese peroxidase, MnP) in a H202-dependent process (57, 58). However, due to extreme complexity of the problem, a vast amount of research needs to be done to understand all the factors involved in lignin biodegradation process (59).