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Stage-structured plastisphere succession sustains antibiotic resistomes on microplastics during full-scale A2/O wastewater treatment
Summary
Tiny bits of plastic that pass through wastewater treatment plants can act like rafts for bacteria carrying antibiotic-resistance genes, and this study found that these "plastic-riding" microbial communities stay more stable and hold onto resistance genes better than bacteria floating freely in the water. That means treated wastewater released into rivers and lakes may still carry microplastic-linked antibiotic-resistant bacteria, which could contribute to the spread of hard-to-treat infections in the environment.
Wastewater treatment plants (WWTPs) efficiently remove microplastics (MPs), yet residual MPs in high-volume effluents may remain environmentally relevant. Whether MP-associated plastisphere communities undergo succession distinct from the water phase during sequential treatment, and how this affects antibiotic resistance genes (ARGs) and their potential hosts, remains unclear. Here, environmental plastic fragments were sequentially exposed to 12 units of a full-scale A/O WWTP, with contemporaneously collected water-phase samples used for comparison. By integrating 16S rRNA gene sequencing, metagenomics, HT-qPCR-based absolute quantification, metagenome-assembled genome (MAG)-based host inference and water-quality association analysis, we characterized bacterial succession, resistome dynamics, potential ARG hosts, and their associations with environmental factors. Water-phase communities and resistomes showed strong unit-specific fluctuations, reflecting responses to influent inputs, floc formation and removal, filtration, and disinfection. In contrast, the plastisphere exhibited more stage-structured succession, higher community stability, and stronger ARG continuity. Among 276 recovered MAGs, 270 were identified as potential ARG hosts. Several potential ARG hosts with relatively high ARG burdens, including Enterobacteriaceae-affiliated MAGs, showed relative maintenance on MP surfaces during later treatment stages, with dynamics closely tracking ARG changes. Oxygen-pH and nitrogen-related factors were strongly associated with the plastisphere resistome and showed more consistent associations with plastisphere ARGs and potential hosts than in the water phase. These findings suggest that the observed ARG continuity in the plastisphere may be associated with relatively stable microbial communities and the retention of ARG-associated potential hosts, indicating possible residual MP-associated resistome risks in treated effluent.