Fe-doped TiO2 nanosheet exposure accelerates the spread of antibiotic resistance genes by promoting plasmid-mediated conjugative transfer

The widespread dissemination of antibiotic resistance genes (ARGs) via plasmid-mediated conjugation poses a serious threat to public health. Conjugation can be accelerated by selective pressures caused by antibiotics and other environmental pollutants. Fe-doped TiO₂ nanosheets (FTNs) are widely used for the photocatalytic treatment of wastewater, raising concerns about their potential presence in the environment and their role in exerting selective pressure on conjugation. In this study, FTNs at subinhibitory concentrations (25, 50, and 100 mg/L) were applied in an in vitro conjugation model to investigate their impact on ARG conjugation. The results showed that FTN exposure increased conjugative transfer frequency by more than 2.5-fold. Molecular mechanism analysis revealed that FTNs increased membrane permeability by causing physical damage and inducing oxidative stress, promoted energy supply by modulating the proton motive force (PMF) and enhancing the tricarboxylic acid (TCA) cycle, and improved intercellular contact by enhancing cell adhesion. Additionally, transcriptomic analysis indicated that FTNs upregulated the expression of genes related to energy supply, cell adhesion, cell transport and oxidative stress. Overall, the findings of this study reveal the potential risk of nanosheets accelerating the spread of ARGs via plasmid-mediated conjugation, highlighting the necessity of establishing guidelines for their appropriate use and discharge.