Study On The Characteristics Of ARGs Distribution In River And Groundwater After Reclaimed Water Recharged

As a kind of emerging pollutants,Antibiotic resistance genes(ARGs)can spread through horizontal gene transfer(HGT)which is distinguish it with normal pollutants.HGT is the main reason for the prevalence of ARGs in the natural environment.With HGT the ARGs can transfer between microorganisms and even from microorganisms to humans,which might threaten safety of the environment and human health.ARGs might enter the groundwater during the process of reclaimed water applied in water supply.To develop a better understanding of the distribution and transmission of ARGs during the recharge process,a field study on the seasonal variations occurrence and concentration of ARGs was conducted in Chaobai River of Beijing.Surface water samples collected,together with soil and groundwater samples were analyzed for the distribution of ARGs(sul1,sul2,dfrA1,dfrA12,tetB,tetO,tetW,tetM).The impacts of the principal selection pressure on the transmission of ARGs during the process of reclaimed water recharging were studied using soil columns and U-tube.Overall,the detection rates of the target genes were 100%except tetO and tet B.The abundant order of ARGs followed sulfonamides resistance genes>methoprim resistance genes>Tetracycline resistance genes in the surface water samples.Gene sul2 was detected with the highest relative abundance in the study area.Seasonal variations appeared in all water samples,followed summer>autumn>spring>winter.Analysis of the ARGs distribution along the vertical direction showed that the order of ARGs in groundwater was consistent within reclaimed water.In general,sul2,sul1,and intI1should be the primary controlled genes in the study area.Pass synthesises analysis of surface water samples indicated that the recharge of reclaimed water caused a certain influence on the surface water.The results of high-throughput sequencing indicated that the relative abundance of Pseudomonas was highest in surface water,and the species diversity was higher in summer and autumn than in spring and winter.Statistical analysis showed that intI1 had a significant correlation with most of ARGs,R~2 up to 0.974.And there was a correlation between various microbial species and abundance of ARGs,especially Acinetobacter in summer and autumn.Principal component analysis in different environment medium showed that the main factor of ARGs is intI1,Sulfamethoxazole,Trimethoprim and Cu,Zn in the studied area.The soil column simulation results showed that the possibility of extracellular ARGs(eARGs)enters into the groundwater system through the soil layer might be greater than antibiotic resistance bacteria(ARB).Meanwhile,the soil column results also pointed out that,as a key factor in the propagation ARGs in environment,HGT may occur in the process of reclaimed water recharging and needs further in-depth study.Transconjugations in the system with eARGs(plasmid RP4)as donor were obtained using modified U-tube experiments.The transfer rate caused by eARGs accounted for up to 7.29%of the total conjugate transfer.HGT under different environmental selective pressures were studied through this device,which suggested that multiple selection stress promoted the HGT of eARGs.The sequencing analysis indicated that the community abundance tansconjugations in RP4 system was higher than the ARB system.Furthermore,the adsorption of exogenous ARGs in soil can increased the probability of ARGs in environments.