RAPID POLYETHER CLEAVAGE VIA EXTRACELLULAR ONE-ELECTRON OXIDATION BY A BROWN-ROT BASIDIOEMYCETE

Fungi that cause brown rot of wood are essential biomass recyclers and also the principal agents of decay in wooden structures, but the extr acellular mechanisms by which they degrade lignocellulose remain unkno wn. To test the hypothesis that brown-rot fungi use extracellular free radical oxidants as biodegradative tools, Gloeophyllum trabeum was ex amined for its ability to depolymerize an environmentally recalcitrant polyether, poly(ethylene oxide) (PEO), that cannot penetrate cell mem branes. Analyses of degraded PEOs by gel permeation chromatography sho wed that the fungus cleaved PEO rapidly by an endo route. C-13 NMR ana lyses of unlabeled and perdeuterated PEOs recovered from G. trabeum cu ltures showed that a major route for depolymerization was oxidative C- C bond cleavage, a reaction diagnostic for hydrogen abstraction from a PEO methylene group by a radical oxidant. Fenton reagent (Fe(II)/H2O2 ) oxidized PEO by the same route in vitro and therefore might account for PEO biodegradation if it is produced by the fungus, but the data d o not rule out involvement of less reactive radicals. The reactivity a nd extrahyphal location of this PEG-degrading system suggest that its natural function is to participate in the brown rot of wood and that i t may enable brown-rot fungi to degrade recalcitrant organopollutants.