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.