Antibiotic Resistance Gene-Carrying Plasmid Spreads into the Plant Endophytic Bacteria using Soil Bacteria as Carriers

Applications of animal manure and treated wastewater could enrich antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs) in the plant microbiome. However, the mechanistic studies of the transmission of ARB and ARGs from the environment to plant endophytic bacteria were few. Herein, a genetically engineered fluorescent Escherichia coli harboring a conjugative RP4 plasmid that carries three ARGs was used to trace its spread into Arabidopsis thaliana interior in a tetracycline-amended hydroponic system in the absence or presence of a simulated soil bacterial community. Confocal microscope observation demonstrated that E. coli was internalized into plant tissues and the carried RP4 plasmid was transferred into plant endophytic bacteria. More importantly, we observed that soil bacteria inhibited the internalization of E. coli but substantially promoted RP4 plasmid spread into the plant microbiome. The altered RP4-carrying bacterial community composition in the plant microbiome and the increased core-shared RP4-carrying bacteria number between plant interior and exterior in the presence of soil bacteria collectively confirmed that soil bacteria, especially Proteobacteria, might capture RP4 from E. coli and then translocate into plant microbiome, resulting in the increased RP4 plasmid spread in the plant endophytes. Overall, our findings provided important insights into the dissemination of ARB and ARGs from the environment to the plant microbiome.