Graphene oxide degradation by a white-rot fungus occurs in spite of lignin peroxidase inhibition

This study investigated the degradation of graphene oxide (GO) by the white-rot fungus Phanerochaete chrysosporium. Axenic fungal suspensions were inoculated in malt extract glucose medium enriched with various concentrations of GO and allowed to grow for several months. Biomass, pH, H2O2 content and activity of laccase (Lac) and lignin peroxidase (LiP) in the culture media were monitored, along with the physicochemical changes of GO over time followed by TEM, Raman, XPS and TGA. Lower concentrations of GO exhibited a stronger stimulating effect on P. chrysosporium growth and the production of Lac and H2O2 compared to higher concentrations, probably due to an excessive parallel increase in GO degradation by-products. The fungus significantly altered the structure of GO, with increase in the Raman D band, although GO neutralized LiP activity, possibly by unspecific adsorption. The activity of isolated LiP, but not of Lac, was suppressed in the presence of GO. Moreover, Lac caused modifications in the GO lattice as evidenced by a significant increase in the ratio between the intensity of the D and G bands of the Raman spectra. This enzyme emerges as a key player in the biodegradation of GRMs within terrestrial ecosystems, as its release extends beyond fungi to several other microorganisms.