Elevated CO2 alters antibiotic resistome in soil amended with sulfamethazine via chemical-organic fertilization.

Rising antimicrobial resistance (AMR) is an enormous challenge for global healthcare systems. The effects of elevated CO2 (eCO2) on AMR are poorly characterized. Using a free-air CO2 enrichment system and high-throughput qPCR arrays, we investigated the response of soil antibiotic resistome and bacterial communities to eCO2 (ambient + 200 ppm) in soils amended with sulfamethazine (SMZ) at 0.1 and 1 mg kg-1 via chemical-organic fertilizer (COL, COH). Results showed that under ambient condition, COH significantly enhanced the diversity of high-risk antibiotic resistance genes (ARGs), relative abundance of low risk ARGs, unassessed ARGs and total ARGs compared to COL. Nevertheless, eCO2 mitigated the effects of COH, with no significant difference found between COL and COH on the above high risk, low risk, unassessed and total ARGs. Meanwhile, eCO2 decreased the relative abundance of spcN, ermA, olec, oprD, sulA-olP, tetB, tetT and vanXD in COL, and alleviated the enrichment of pikR2, ampC, lunC, oprD and pncA caused by the application of SMZ at 1 mg kg-1. Correlation and network analysis illustrated that changes of certain bacteria biomarkers and horizontal gene transfer of integrase gene were associated with the altered response of ARGs abundance to eCO2. This study adds knowledge of the potential risk of antibiotic resistance in agricultural exposure scenarios under increasing CO2 concentration.