Study On The Mechanism Of Nano-TiO₂ Promoting Phage-Mediated Horizontal Transfer Of Antibiotic Resistance Genes

In recent years,the abuse of antibiotics has led to the continuous spread of antibiotic resistance genes?ARGs?into the environment,which has caused increasingly serious health risks and environmental pollution.The spread of ARGs has attracted much attention in environmental studies.The impact of environmental factors on ARGs spread gradually becomes a research hotspot of environmental science.Although nanomaterials have been proved to promote the horizontal transfer of ARGs through conjugation and transformation,whether it can be conducive to ARGs spread mediated by phage transduction is still not reported.Therefore,in this paper,nano-TiO₂,phage gM13 and E.coli TG1 were used as a transduction model to explore the influence of nano-TiO₂ itself and its photoexcitation on phage gM13infecting E.coli TG1.Meanwhile,the mechanism of nano-TiO₂ promoting phage-mediated ARGs transduction was also futher investigated.The following preliminary conclusions were obtained in this study:?1?Nano-TiO₂ could significantly improve phage infecting bacteria.The transduction efficiency reached the highest in treatment with 0.5 mM nano-TiO₂,which was 4.5 times of the control treatment without nano-TiO₂.Nano-TiO₂ with particle sizes of 20 and 50 nm showed higher stimulating effect on ARGs transduction than of 5 and 100 nm.Prolonging the infection time and increasing the number of phages both could promote ARGs transfer.Nano-TiO₂ displayed good hydrophilicity,which was conducive to attaching to the bacterial surface and attracting phages to aggregate around bacteria.?2?Nano-TiO₂ exposure triggered oxidative stress reaction of bacteria and increased intracellular ROS level,which could reduce the stability of outer membrane and contribute to gM13 phage infection.Meanwhile,nano-TiO₂ increased the activity of intracellular antioxidase and significantly promoted the expression of F-pili related genes?e.g.traA,traX and traV?,which could contribute to the contact between cells and phage and enhance the transduction efficiency of ARGs.?3?Photoexcitation of nano-TiO₂ could significantly promote phage infection.The transduction efficiency of the bacteriophage was increased by 4.6 times and 8.6times by the treatment with nano-TiO₂ or UV alone,respectively.The transduction efficiency of phages could be increased by 21.4 times when nano-TiO₂ was excitated by UV,which showed a significantly synergistic effect on the bacteriophage infection.?4?Extracellular ROS produced by nano-TiO₂ photoexcitation contributed to the phage-mediated ARGs transduction.Meanwhile,nano-TiO₂ photoexcitation could also induce bacterial oxidative stress system,increase the intracellular ROS level,increase cell membrane permeability and promote the expression of pili-related genes,which further resulted in the increase of gM13 phage infection.