Prevalence of antibiotic resistance gene in different wastewater treatment systems and effluent-irrigated soils through metagenomic analysis

Wastewater treatment systems (WWTS) are considered to be the main source of antibiotic resistance genes (ARGs) spreading into the environment. In this study, samples were collected from WWTS influent, biological treatment tank effluent, and recycled water treatment plant (RTP) effluent during summer and winter, followed by metagenomic sequencing. The study investigated the differences in antibiotic resistance gene transfer between two typical wastewater treatment plants (WWTPs) processes and the impact of recycled water irrigation on ARG dissemination in soil. The WWTS (HD and MD) adopting two combined processes of "Adsorption-Biodegradation Process(AB )+ Anaerobic-Anoxic-Oxic Process(AAO)" and "AAO + Membrane Bioreactor(MBR)" as the research objects for the first time.The primary ARGs types identified were multidrug resistance, tetracycline, macrolide, and aminoglycoside resistance genes. The top three ARGs subtypes by relative abundance in the influent, biological treatment tank effluent, and total effluent were msrE, mphE, and ANT(6)-Ia, respectively. Seasonal variations did not significantly influence the distribution of ARGs in the two WWTSs. The AAO and AB processes increase the relative abundance and diversity of ARGs, while ARGs relative abundance decreases after RTP treatment but may proliferate new ARGs subtypes. Additionally, the efficiency of reducing the relative abundance of ARGs in summer is higher than that in winter. The two WWTSs were able to efficiently remove msrE and mphE. The abundance and diversity of ARGs and microorganisms were maximum in soil samples from the RTP. The microbial genera significantly related to ARGs may become its potential host, such as Rhodanobacter had significant correlations with ropB2, carA, and oleB. These results provide new insights into the control of ARGs contamination and focus on the risks associated with irrigated wastewater.