Plastic Biodegradation by Sediment Microbial Populations under Denitrifying Conditions

Biodegradation is critical for eliminating plastic contaminants from environments, and understanding its mechanisms under in situ conditions is crucial. The plastic biodegradation process in sediments, a major reservoir of plastic contamination with reduced redox conditions, remains elusive. This study compared the plastisphere communities and metabolic potentials of typical polyethylene (PE) contaminants collected from the Pearl River Estuary to their counterparts in the surrounding sediments. The results revealed a distinct plastisphere community composition, with the consistent enrichment of a group of core plastisphere populations compared to those of the sediments. Functional genes related to both potential aerobic and anaerobic PE biodegradation were encoded by the core plastisphere populations. Microcosm incubations were performed to assess the PE biodegradation potentials under denitrifying conditions. The results demonstrated that the polyethylene (PE) mineralization efficiencies were comparable under aerobic and denitrifying conditions through incubations with 13C-PE. Development of functional groups on PE surfaces and the reduction in molecular weights further supported PE biodegradation under denitrifying conditions. The elevated laccase and lignin peroxidase activities implied their potential contribution to PE depolymerization under denitrifying conditions. Together, the sediment plastisphere microbiome holds the potential for plastic degradation under denitrifying conditions, which should be considered when assessing the fate of plastic contaminants.