Unveiling the characteristics of free-living and particle-associated antibiotic resistance genes associated with bacterial communities along different processes in a full-scale drinking water treatment plant

Abstract

Antibiotic resistance genes (ARGs) as emerging contaminants, often co-occur with mobile genetic elements (MGEs) and are prevalent in drinking water treatment plants (DWTPs). In this study, the characteristics of free-living (FL) and particle-associated (PA) ARGs associated with bacterial communities were investigated along two processes within a full-scale DWTP. A total of 13 ARGs and two MGEs were detected. FL-ARGs with diverse subtypes and PA-ARGs with high abundances displayed significantly different structures. PA-MGEs showed a strong positive correlation with PA-ARGs. Chlorine dioxide disinfection achieved 1.47-log reduction of FL-MGEs in process A and 0.24-log reduction of PA-MGEs in process B. Notably, PA-fraction virtually disappeared after treatment, while blaTEM, sul2, mexE, mexF and IntI1 of FL-fraction remained in the finished water. Moreover, Acinetobacter lwoffii (0.04% ~ 45.58%) and Acinetobacter schindleri (0.00% ~ 18.54%) dominated the 16 pathogens, which were more abundant in FL than PA bacterial communities. PA bacteria exhibited a more complex structure with more keystone species than FL bacteria. MGEs contributed 20.23% and 19.31% to the changes of FL-ARGs and PA-ARGs respectively, and water quality was a key driver (21.73%) for PA-ARGs variation. This study provides novel insights into microbial risk control associated with size-fractionated ARGs in drinking water. Environmental implicationAntibiotic resistance genes (ARGs) can be considered as “hazardous materials”, since their occurrence and transmission are harmful to ecological environment and threaten public health, especially in drinking water. This study demonstrated the different characteristics between the free-living (FL) and particle-associated (PA) ARGs along the drinking water treatment processes, from the perspective of structures, interactions and bacterial hosts (including pathogenic species). Process units showed discrepant effects on size-fractionated ARGs, and some FL-ARGs remained in the finished water. These findings can deepen our understanding of ARG transmission mechanisms, and help optimize size-fractionated ARGs control strategies to ensure microbial safety in drinking water.