Ligninolysis: Roles of Microbes and Their Extracellular Enzymes

Biodegradation of lignin, one of the most abundant components of lignocellulosic plant biomass, represents a key step for carbon recycling. The structure of lignin, however, makes it recalcitrant to degradation. This correlates both to environmental issues and agroindustrial utilization of lignocellulosic plant biomass. By cross-linking to both cellulose and hemicellulose, lignin forms a barrier that prevents the accessibility of chemicals or lignocellulolytic enzymes into the interior of lignocellulosic structure. The presence of lignin negatively affects the utility of cellulose in pulp and paper industry, textile industry, biofuel production, as well as animal feed. To improve the bioprocessing of lignocellulosic feedstocks in various industries, more effective degradation methods of lignin are in high demand. Some microbes are able to efficiently degrade lignin using a combination of extracellular ligninolytic enzymes, organic acids, mediators, and several accessory enzymes. Exploring the range of ligninolytic microbial biodiversity is the key to developing effective and eco-friendly strategies for environmental restoration or optimal and sustainable agroindustrial utilization of plant biomass. This study gives an insight of ligninolytic microbes and the extracellular enzymes implicated in lignin degradation.