Silver nanoparticles facilitate phage-borne resistance gene transfer in planktonic and microplastic-attached bacteria

The spread of bacteriophage-borne antibiotic resistance genes (ARGs) poses a realistic threat to human health. Nanomaterials, as important emerging pollutants, have potential impacts on ARGs dissemination in aquatic environments. However, little is known about its role in transductive transfer of ARGs mediated by bacteriophage in the presence of microplastics. Therefore, this study comprehensively investigated the influence of silver nanoparticles (AgNPs) on the transfer of bacteriophage-encoded ARGs in planktonic Escherichia coli and microplastic-attached biofilm. AgNPs exposure facilitated the phage transduction in planktonic and microplastic-attached bacteria at ambient concentration of 0.1 mg/L. Biological binding mediated by phage-specific recognition, rather than physical aggregation conducted by hydrophilicity and ζ-potential, dominated the bacterial adhesion of AgNPs. The aggregated AgNPs in turn resulted in elevated oxidative stress and membrane destabilization, which promoted the bacteriophage infection to planktonic bacteria. AgNPs exposure could disrupt colanic acid biosynthesis and then reduce the thickness of biofilm on microplastics, contributing to the transfer of phage-encoded ARGs. Moreover, the roughness of microplastics also affected the performance of AgNPs on the transductive transfer of ARGs in biofilms. This study reveals the compound risks of nanomaterials and microplastics in phage-borne ARGs dissemination and highlights the complexity in various environmental scenarios.

TiO2 photoexcitation promoted horizontal transfer of resistance genes mediated by phage transduction

Environmental pollution caused by antibiotic resistance genes (ARGs) has attracted wide concerns, and various approaches have been proposed to control ARGs dissemination. TiO₂ photoexcitation under UV irradiation has been used for such a purpose. But the actual UV intensity is insufficient to trigger the production of reactive oxygen species (ROS) in the aqueous environment. Thus, it is interesting to know how mild photoexcitation of TiO₂ with low-intensity UV affects the horizontal transfer of ARGs. In this work, the impact of TiO₂ photoexcitation on the transductant efficiency of constructed filamentous phage gM13 to its host Escherichia coli TG1 was investigated. Although individual treatment with nano-TiO₂ and UV irradiation both improved the phage infection, TiO₂ photoexcitation exhibited a clear synergistic promotion effect. However, excessive UV irradiation resulted in a decrease in transductant formation, implying severe oxidative damage to the phage and bacterial cells. Extracellular ROS produced by moderate photoexcitation of TiO₂ could increase the outer membrane permeability, which facilitated phage infection. The increase in pili synthesis induced by intracellular ROS provided more sites for phage recognition and invasion in the presence of TiO₂ photoexcitation, which contributed to the transduction process. Our work provides a novel insight into the impact of TiO₂ photoexcitation on ARGs diffusion and is helpful for better understanding non-toxic environmental effect of nanomaterials.