Elevated CO2 alleviated the dissemination of antibiotic resistance genes in sulfadiazine-contaminated soil: A free-air CO2 enrichment study.

Climate change affects soil microbial communities and their genetic exchange, and subsequently modifies the transfer of antibiotic resistance genes (ARGs) among bacteria. However, how elevated CO2 impacts soil antibiotic resistome remains poorly characterized. Here, a free-air CO2 enrichment system was used in the field to investigate the responses of ARGs profiles and bacterial communities to elevated CO2 (+200 ppm) in soils amended with sulfadiazine (SDZ) at 0, 0.5 and 5 mg kg-1. Results showed that SDZ exposure induced the co-occurrence of beta-lactamase and tetracycline resistance genes, and SDZ at 5 mg kg-1 enhanced the abundance of aminoglycoside, sulfonamide and multidrug resistance genes. However, elevated CO2 weakened the effects of SDZ at 0.5 mg kg-1 following an observed reduction in the total abundance of ARGs and mobile genetic elements. Additionally, elevated CO2 significantly decreased the abundance of vancomycin resistance genes and alleviated the stimulation of SDZ on the dissemination of aminoglycoside resistance genes. Correlation analysis and structural equation models revealed that elevated CO2 could directly influence the spread of ARGs or impose indirect effects on ARGs by affecting soil properties and bacterial communities. Overall, our results furthered the knowledge of the dissemination risks of ARGs under future climate scenarios.