Polyethylene degradation and assimilation by the marine yeast <i>Rhodotorula mucilaginosa</i>

Ocean plastic pollution is a severe environmental problem but most of the plastic that has been released to the ocean since the 1950s is unaccounted for. Although fungal degradation of marine plastics has been suggested as a potential sink mechanism, unambiguous proof of plastic degradation by marine fungi, or other microbes, is scarce. Here we applied stable isotope tracing assays with ¹³C-labeled polyethylene to measure biodegradation rates and to trace the incorporation of plastic-derived carbon into individual cells of the yeast Rhodotorula mucilaginosa, which we isolated from the marine environment. ¹³C accumulation in the CO₂ pool during 5-day incubation experiments with R. mucilaginosa and UV-irradiated ¹³C-labeled polyethylene as a sole energy and carbon source translated to degradation rates of 3.8% yr^-1 of the initially added substrate. Furthermore, nanoSIMS measurements revealed substantial incorporation of polyethylene-derived carbon into fungal biomass. Our results demonstrate the potential of R. mucilaginosa to mineralize and assimilate carbon from plastics and suggest that fungal plastic degradation may be an important sink for polyethylene litter in the marine environment.