Differential profiles of antibiotic resistance genes in activated sludge and biofilm in wastewater treatment plants

Wastewater treatment plants (WWTPs) serve as significant sources of antibiotic resistance genes (ARGs) in natural water bodies, with activated sludge and biofilm being the two most critical biological treatment processes in WWTPs. A systematic comparison of ARG composition in these two processes is essential for optimizing the design and operation of wastewater treatment systems. This study collected samples from 16 WWTPs, including one year of longitudinal monitoring data from a full-scale facility and encompassing five biofilm types. The high-throughput sequencing results revealed that the relative abundance of ARGs in activated sludge was significantly higher than in biofilms, with average relative abundances of 2075.05 ppm and 1288.78 ppm, respectively. We also identified plasmids and microbial community structure as key factors contributing to the differences in ARG composition between activated sludge and biofilm. Plasmids primarily influenced the ARGs associated with enzymatic modification mechanisms, while the microbial community structure mainly impacted the abundance of ARGs, particularly through its effect on Bacteroidia. This structural influence was particularly pronounced on ARGs related to enzymatic inactivation, enzymatic modification, efflux pumps, target modification, and target protection mechanisms. These findings provide valuable insights for improving the management of ARGs in WWTPs and contribute to the development of strategies for mitigating ARG proliferation in wastewater treatment systems.