Abstract
Lignin is the second most abundant biopolymer and the largest reservoir of bio-based aromatic building blocks on earth that could replace numerous products currently produced from fossil feedstock with more sustainable, bio-based alternatives. However, its large-scale exploitation for value creation beyond its current main use in energy applications is hampered by its natural inertness and structural complexity and the highly denatured state of the bulk of technical lignin available as a by-product of large-scale processing of lignocellulose in the pulp and paper industry. In this section, we outline current paths of lignin valorization for value creation with a focus on enzymatic processing. Microbial sources and the current status of knowledge of the most important classes of ligninolytic enzymes are presented, as are options for new enzyme discovery and possible approaches to solve some of the key challenges of efficient enzymatic depolymerization of lignin to derive compounds directly marketable as value-added chemicals or usable as a feedstock for further upgrading by microbial metabolism to bio-based fuels, chemicals, and materials.