Biodegradable and non-biodegradable plastics foster unique regimes of antibiotic resistance and virulence factors in aquatic plastispheres

The plastisphere, the biofilm community on plastic debris, is recognized as a reservoir for antibiotic resistance genes (ARGs) and pathogens. However, the comparative risks of biodegradable (BPs) versus non-biodegradable (non-BPs) plastics remain unclear. This study tested the hypothesis that BPs and non-BPs foster distinct risk trajectories through distinct underlying mechanisms. We investigated microbial succession and the fate of ARGs and virulence factors (VFs) on polylactic acid (PLA, one of the BPs), polyvinyl chloride (PVC), and polystyrene (PS) during an 88-day in situ incubation in a tidal river. Metagenomic analysis revealed that PVC consistently harbored the highest abundance of ARGs and mobile genetic elements (MGEs), acting as a persistent hub for resistance, with multidrug resistance genes enriched up to 3.5-fold compared with river water. In contrast, the biodegradable PLA exhibited a distinctly transient risk profile during the mid-degradation stage, creating a hotspot for opportunistic pathogenic genera like Vibrio and Acinetobacter, coinciding with a significant spike in ARGs' abundance. Genome-resolved metagenomics further confirmed the co-localization of ARGs and VFs within high-risk metagenome-assembled genomes (MAGs). These findings demonstrate that both BPs and non-BPs pose significant but fundamentally different risks of ARGs and VFs. Risk assessments must therefore consider the entire lifecycle of plastics, accounting for the transient, degradation-driven hazards posed by BPs and the persistent, accumulative threats posed by non-BPs.