Generation of extracellular antibiotic resistance genes during municipal wastewater chlorination and UV disinfection

In this study, the generation of eARGs in different physical forms during wastewater chlorination and ultraviolet (UV) disinfection was investigated, and the correlation with microbial communities was explored. Results indicated that though chlorination decreased the abundance of intracellular ARGs, absorbed eARGs was significantly amplified by (0.7±0.1)log, while the abundance of free eARGs decreased by (0.2±0.1)log. UV disinfection also decreased the abundance of intracellular ARGs, but caused a significant increase of free eARGs ((0.4±0.2)log) and a decrease of absorbed eARGs ((0.3±0.1)log). Post chlorination, the abundance of most phyla increased while Proteobacteria decreased in the absorbed extracellular DNA (a-eDNA), resulting in a increase of the bacterial diversity index from 4.2 to 4.7. Whereas, Proteobacteria increased by 6.6% in the free extracellular DNA (f-eDNA) after chlorination, causing a decrease of the bacterial diversity index from 3.5 to 2.8. Post UV disinfection, the abundance of Proteobacteria in a-eDNA decreased by 36.6%, while the bacterial diversity index increased to 4.8; the abundance of bacteria in f-eDNA changed slightly. The molecular ecological network analysis indicated a wide hosting relationship between ARGs and bacteria genera. tetA, tetX, sulI and sulII were correlated with 17, 15, 15 and 5genera respectively, suggesting changes in potential hosts post disinfection were essential mechanisms of the eARGs generation. This study shows that chlorination and UV disinfection can't eliminate the risk of antibiotic resistance but only change patterns of the risk by inducing the generation of adsorbed and free eARGs. © 2021, Editorial Board of China Environmental Science. All right reserved.