Key Takeaways & Executive Findings
- •• • PS-COOH (0.1–20 mg·L−1) promotes eARG transformation in a dose-dependent manner, increasing the environmental spread of antibiotic resistance in aquatic systems. • • Low PS-NH2 (0.1–0.5 mg·L−1) enhances transformation more strongly than PS-COOH at equal concentrations, while high PS-NH2 (1–20 mg·L−1) inhibits it, indicating a concentration-dependent dual effect. • • Promotion correlates with increased intracellular ROS, membrane permeability, and EPS protein/polysaccharide ratio, while inhibition involves ROS-induced cell lysis and plasmid aggregation. • • Both PS-COOH and low PS-NH2 stimulate biofilm formation, which can further amplify ARG dissemination in natural and engineered water systems.
Abstract
The rapid dissemination of antibiotic resistance genes (ARGs) in aquatic environments poses serious threats to public health and environmental safety under the 'One Health' framework. Nanoplastics (NPs), as co-occurring pollutants, can exacerbate ARG risks by promoting horizontal gene transfer (HGT), yet the influence of different functional groups on extracellular ARG (eARG) transformation remains unclear. This study investigated the effects of carboxy-modified polystyrene NPs (PS-COOH) and amino-functionalized polystyrene NPs (PS-NH2) compared to unmodified polystyrene NPs (PS) on the transformation of the extracellular resistance plasmid IE-V1955 (carrying an ampicillin resistance gene) into Escherichia coli DH5α. Results showed that PS-COOH exposure promoted plasmid transformation similarly to PS, with effects increasing over 0.1–20 mg·L−1. Low concentrations (0.1–0.5 mg·L−1) of PS-NH2 also enhanced transformation, with stronger effects than PS-COOH at equal doses, whereas high concentrations (1–20 mg·L−1) inhibited it. Mechanistically, PS-COOH (0.1–20 mg·L−1) and low PS-NH2 induced intracellular reactive oxygen species (ROS), increased cell membrane permeability, elevated the protein-to-polysaccharide ratio in extracellular polymeric substances (EPS), and promoted biofilm formation, thereby facilitating transformation. High PS-NH2 concentrations caused excessive ROS leading to cell lysis and formed aggregates with plasmids larger than membrane pores, blocking uptake. These findings provide a theoretical basis for assessing the combined environmental health risks of NPs and ARGs.
1. Introduction
Antibiotic resistance genes (ARGs) are emerging environmental contaminants that undermine the efficacy of antibiotics, posing a critical challenge to public health. Horizontal gene transfer (HGT) via natural transformation is a primary mechanism for ARG dissemination in aquatic environments. Co-occurring nanoplastics (NPs), ubiquitous in water bodies, have been shown to facilitate HGT, yet the influence of surface functional groups—common in environmental NPs due to weathering or industrial modification—on this process remains poorly understood. Existing studies have largely focused on pristine NPs, overlooking the differential effects of carboxyl and amino groups that alter surface charge and reactivity.
This study addresses this gap by systematically comparing the effects of carboxy-modified (PS-COOH) and amino-modified (PS-NH2) polystyrene NPs against unmodified PS on the transformation of a model extracellular plasmid into E. coli. By quantifying transformation frequencies and dissecting mechanistic pathways involving oxidative stress, membrane integrity, and biofilm formation, the research provides critical data for risk assessment of NP-ARG co-contamination. The findings reveal a concentration-dependent, functional-group-specific modulation of eARG uptake, highlighting the need to consider NP surface chemistry in evaluating environmental health risks.
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WEI Zihan, SHAO Mengying, LIU Bingjie, LIU Yifan, MA Xiaohan, LIU Liuqingqing, LUO Xianxiang, LI Fengmin, ZHENG Hao (2026). Effects of Different Functionalized Nanoplastics on the Transformation of Extracellular Antibiotic Resistance Genes in Aquatic Environments. Environmental Chemistry. https://doi.org/10.7524/j.issn.0254-6108.2024112804
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Frequently Asked Questions
What are the specific concentration thresholds for the dual effect of PS-NH2 on eARG transformation?
Low concentrations of PS-NH2 (0.1–0.5 mg·L−1) promote transformation, while high concentrations (1–20 mg·L−1) inhibit it, as demonstrated in this study.
How does PS-COOH exposure affect eARG transformation compared to unmodified PS?
PS-COOH promotes transformation similarly to PS, with the effect increasing with concentration from 0.1 to 20 mg·L−1.
What are the underlying mechanisms for the promotion of eARG transformation by PS-COOH and low PS-NH2?
Promotion is associated with increased intracellular ROS, enhanced cell membrane permeability, elevated EPS protein/polysaccharide ratio, and stimulated biofilm formation.
What mechanisms explain the inhibitory effect of high PS-NH2 concentrations?
High PS-NH2 induces excessive ROS leading to cell lysis and forms aggregates with plasmids that are larger than membrane pores, thereby blocking plasmid uptake.
What are the environmental implications of these findings for ARG dissemination?
The study indicates that functionalized nanoplastics can modulate eARG transformation in a concentration- and functional-group-dependent manner, potentially influencing the spread of antibiotic resistance in aquatic environments.
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