Co-effect of cadmium and iron oxide nanoparticles on plasmid-mediated conjugative transfer of antibiotic resistance genes

•Co-exposure of nano Fe2O3 and Cd2+ significantly promotes transfer of RP4 plasmid.•Antioxidant enzyme activities were enhanced by Cd2+-nano Fe2O3 treatment.•Bacterial cell permeability and conjugation genes expression were accelerated.•The majority of transconjugants were identified to be human pathogens. Conjunctive transfer of antibiotic resistance genes (ARGs) among bacteria driven by plasmids facilitated the evolution and spread of antibiotic resistance. Heavy metal exposure accelerated the plasmid-mediated conjunctive transfer of ARGs. Nanomaterials are well-known adsorbents for heavy metals removal, with the capability of combatting resistant bacteria/facilitating conjunctive transfer of ARGs. However, co-effect of heavy metals and nanomaterials on plasmid-mediated conjunctive transfer of ARGs was still unknown. In this study, we investigated the effect of the simultaneous exposure of Cd2+ and nano Fe2O3 on conjugative transfer of plasmid RP4 from Pseudomonas putida KT2442 to water microbial community. The permeability of bacterial cell membranes, antioxidant enzyme activities and conjugation gene expression were also investigated. The results suggested that the combination of Cd2+ and high concentration nano Fe2O3 (10 mg/L and 100 mg/L) significantly increased conjugative transfer frequencies of RP4 plasmid (p