Effects of cations and nanoparticles on the antibiotic-resistance gene transformation of Escherichia coli at different time scales

Antibiotic resistance genes (ARGs) can be horizontally transferred when bacterial cells take up environmental DNA and gain the antibiotic resistance, a process referred to as transformation. This study investigated the effects of two major cations (monovalent Na + , divalent Ca 2+ ) and two representative organic (polystyrene nanoparticles, PSNP) and inorganic (silver nanoparticles, AgNP) nanoparticles, on the natural transformation of E. coli . In nanoparticle-free systems, both Na + and Ca 2+ promoted transformation. The effect was stronger at higher ion concentration and in Ca 2+ than in Na + . Ion-induced plasmid conformation change, reduced electrostatic interaction, and cation bridging (for Ca 2+ ) were identified as dominant mechanisms leading to the increased plasmid uptake and transformation, despite decreased membrane permeability. Interestingly, AgNP and PSNP exhibited time-dependent, opposing roles in transformation. At 1.5 hours, AgNP promoted transformation by increasing membrane permeability, while PSNP inhibited it by binding plasmids and preventing uptake. However, over 24 hours, these effects reversed: AgNP inhibited transformation due to accumulating toxicity of dissolved Ag + , whereas PSNP enhanced transformation by increasing membrane permeability through PSNP accumulation. These findings underscore the complex, material-specific, and time-dependent influences of nanoparticles on bacteria transformation, revealing their potential environmental and health implications. • Both Na + and Ca 2+ promoted antibiotic-resistance gene transformation of E.coli . • The promoting effect increased at higher ion concentration and in Ca 2+ than in Na + . • The effect of nanoparticles on transformation depended on NP type and exposure time. • AgNP promoted transformation at shorter time scale but inhibited it at longer time scale. • Nanoplastics inhibited transformation at shorter time scale but promoted it at longer time scale.