Does the herbicide napropamide exhibit enantioselective effects across genus plasmid transfer from Escherichia coli to Bacillus subtilis?

The dissemination of plasmid-borne antibiotic resistance genes (ARGs) into the environment is an urgent concern. However, the enantioselective effects of herbicides on plasmid conjugation among bacterial genera and their underlying mechanisms remain unclear. This study demonstrates for the first time that the herbicide napropamide (NAP), commonly used in vegetable fields, exhibits a concentration-dependent effect on the transfer efficiency of the pBE2R plasmid from Escherichia coli to Bacillus subtilis. Notably, at a concentration of 5 mg L, R-NAP increased transfer efficiency by threefold compared to the S-enantiomer. Scanning electron microscopy revealed that R-NAP caused less structural damage to bacteria than S-NAP but more effectively reduced cell wall components (lipopolysaccharides and peptidoglycan) in donor and recipient bacteria, increasing reactive oxygen species levels and membrane permeability. Transcriptomic analysis indicated that NAP enantiomers altered the expression of genes related to membrane transport activity and transposons. Cross-domain network analysis identified yieK, ygeH, and ydbL as key genes mediating conjugation transfer. Molecular docking results showed that NAP likely interacts hydrophobically with the active sites of the proteins encoded by these genes. In conclusion, herbicides like R-NAP should be carefully managed in fields irrigated with livestock manure to mitigate the risk of ARG transfer and accumulation in crops.