Copper Ions Facilitate the Conjugative Transfer of SXT/R391 Integrative and Conjugative Element Across Bacterial Genera.

Copper can persist stably in the environment for prolonged periods. Except for inducing antibiotic resistance in bacteria, copper ions (Cu) can facilitate the horizontal transfer of plasmid DNA. However, whether and how Cu can accelerate the conjugative transfer of SXT/R391 integrative and conjugative element (ICE) is still largely unknown. In this study, ChSC1905, harboring an SXT/R391 ICE that carried 21 antibiotic resistance genes (ARGs), was used as a donor, and EC600 was used as a recipient. Cu, at subinhibitory and environmentally relevant concentrations (1-10 μmol/L), significantly accelerated the conjugative transfer of SXT/R391 ICE across bacterial genera (from to ) ( < 0.05). The combined analyses of phenotypic tests and genome-wide sequencing indicated that reactive oxygen species (ROS) production and cell membrane permeability were critical in the enhanced conjugative transfer of SXT/R391 ICE. Furthermore, the expression of genes related to cell adhesion and ATP synthesis was also significantly upregulated on exposure to Cu at a concentration of 5 μmol/L. This study clarified the potential mechanisms of Cu to promote the conjugative transfer of SXT/R391 ICE, revealing the potential risk imposed by Cu on the horizontal transfer of SXT/R391 ICE-mediated ARGs.