Bacteria involved in plastic anaerobic degradation in marine sediments under nitrate and iron-reducing conditions

Abstract

Marine sediments are major sinks for microplastics, with concentrations significantly higher than in seawater. However, little is known about the biodegradation of plastic debris in oxygen-deficient sediments. In this study, we characterized the bacteria with the potential for anaerobic degradation of plastics in sediments sampled from the semi-closed Sansha Bay located in the Taiwan Strait. Using common polyhydrocarbon plastics—polyethylene (PE), polypropylene (PP), and polystyrene (PS)—as the sole carbon and energy sources, anaerobic degrading bacteria were enriched under nitrate-reducing and iron-reducing conditions. After incubation, bacterial community analysis based on 16S rRNA sequencing revealed that under iron-reducing conditions, norank_Caulobacteraceae, Ralstonia, Shewanella, and Vibrio were the most abundant core taxa, whereas Shewanella and Vibrio dominated nitrate-reducing communities across all plastic types. Co-occurrence network analysis further indicated that members of Proteobacteria and Desulfobacterota cooperatively contributed to plastic anaerobic degradation. At the genus level, Vibrio was identified as the most prominent keystone taxon alongside Marinobacter. Bacterial isolation and biodegradation assays confirmed Vibrio alginolyticus as an anaerobic degrader under nitrate-reducing conditions, capable of forming biofilms on PE, PP, and PS surfaces and inducing physicochemical deterioration. This study provides the first evidence of bacteria involved in anaerobic plastic degradation in marine environments, underscoring that this process may actively influence the fate of plastic debris and microplastics in marine sediments.