Migration of fungicides, antibiotics and resistome in the soil-lettuce system.

The emergence and spread of antibiotic resistance genes (ARGs) have become a serious issue in global agricultural production. However, understanding how these ARGs spread across different spatial scales, especially when exposed to both pesticides and antibiotics, has remained a challenge. Here, metagenomic assembly and binning methodologies were used to determine the spread pathway of ARGs in the soil-lettuce system under individual and combined exposure of fungicides (carbendazim and pyraclostrobin) and antibiotics (chlortetracycline and ciprofloxacin). These agrochemicals not only facilitated the spread of ARGs from soil to lettuce but also significantly elevated the risk of developing multi-antibiotic resistance among bacteria, especially to some antibiotic types (i.e. sulfonamide, aminoglycoside, quinolone, and tetracycline). ARGs could be migrated through distinct pathways, including both vertical and horizontal gene transfer, with plasmids playing a crucial role in facilitating the horizontal gene transfer. These transfer pathways have enabled key pathogenic bacteria belonging to the genera Acinetobacter, Pseudomonas, and Pantoea to acquire resistance and remain recalcitrant, posing the potential risk to crop health and food safety. In summary, our findings highlighted that fungicide and antibiotic could drive upward migration of ARGs in the soil-lettuce system and reduced the quality safety of agricultural products.