Migration of antibiotic resistance genes in process of biodegradation of sulfonamide antibiotics in biofilm-sediment: Mechanisms, microbial communities, and driving factors.

The main removal pathway of sulfonamide antibiotics (SAs) in biofilm-sediment system is biodegradation, which not only promotes the enrichment of drug-resistant bacteria, but its metabolic intermediates also promote the horizontal gene transfer (HGT) of antibiotic resistance genes (ARGs). Since the biofilm-sediment multiphase system is closer to characteristics of the natural aquatic environment, the study of the dynamic migration process of ARGs in this system can reveal the propagation patterns of ARGs more realistically. Therefore, this study investigated the migration characteristics of ARGs and their driving mechanisms during the biodegradation of SAs in the biofilm-sediment system. The results showed that the migration of ARGs exhibited obvious stratification characteristics: the abundance of ARGs in the surface biofilm fluctuated in synchrony with the degradation of SAs, the HGT mediated by mobile genetic elements (MGEs) in middle sediments enabled the cross-layer migration and accumulation of ARGs, while deep sediments were limited in migration due to hypoxia and pore barriers. Changes in the bacterial community also facilitated the migration of ARGs, with the proliferation of host bacteria dominating the surface layer and the formation of a composite transfer system of "host bacteria-ARGs-MGEs" in the middle layer. The multivariate statistical analysis model confirmed that the synergistic effects of bacterial abundance, MGEs and environmental factors contributed 95-99% to the migration of ARGs in the surface and middle layers, with pH being the strongest positive regulator. These results demonstrated that the migration of ARGs is closely related to the degradation process of pollutants.