Extracellular free radical biochemistry of ligninolytic fungi

Abstract. – Higher filamentous fungi are the primary degraders of lignin in nature. Research has shown that fungi employ several types of free radical chemistry to break down this abundant and recalcitrant wood polymer. Fungal ligninolytic mechanisms play an essential role in global carbon cycling, and may also serve as inspiration for new, environmentally friendly biomimetic catalysts. Lignin is the most abundant aromatic chemical on earth, comprising roughly 15 % of all terrestrial biomass. Formed through the free radical polymerization of several p-hydroxycinnamyl alcohols, it is a heterogeneous, highly crosslinked polymer that encases the structural polysaccharides of higher plant cell walls. The intermonomer linkages of lignin consist of alkyl aryl ether, arylpropane, biphenyl, and other bonds that resist cleavage by most biochemical agents1,2. These properties are consonant with the polymer’s functions, which are to give vascular plants the rigidity the