Strategic Role of Fungal Laccases in Biodegradation of Lignin

Lignin is a complex organic material connecting cells, fibers, and vessels which constitute wood and other lignified components of the vascular plants. Because of its complex structure consolidated by three-dimensional cross-linking, it is highly inflexible and recalcitrant. The degradation of lignin is required for the efficient utilization of lignocellulosic biomass for the production of biofuels and other cellulose-based products. Removal of lignin is also necessary for the production of paper from wood during the process of delignification and bleaching. Existing physico-chemical methods of lignin degradation are cost and energy incentive and result in generation of toxic waste products. Biodegradation of lignin involving lignin-degrading microbes and their enzyme system is more efficient and environmentally sound approach. Biodegradation of lignin is considered as sustainable technology for the disposal of lignocellulosic biomass and its utilization for the production of value-added products. Among microbes, white rot fungi efficiently degrade lignin with the help of their oxidative extracellular ligninolytic enzymes in general and laccases (benzenediol oxygen oxidoreductase, EC 1.10.3.2) in particular. Laccases are multinuclear enzymes which effectively degrade lignin. In the presence of suitable mediators, laccases hold the potential to oxidize non-phenolic proportion of lignin and other substrates. In the backdrop of aforesaid context, this chapter is an attempt to put forth the details of role of fungal laccases and laccase mediator system in degradation of lignin.