Occurrence Characteristics Of ARGs And MGEs In High Standard Sewage Treatment Plants And Correlation To Microbial Community

With the continuous improvement of pollutant discharge standards for sewage treatment plants in China,more and more advanced sewage treatment processes are put into use.Compared with conventional indicators of water pollution such as chemical oxygen demand（COD）,N,P,few studies pay attention to the impact of these advanced treatment processes on antibiotic resistance genes（ARGs）.This article uses metagenomic technology to clarify the distribution characteristics of high emission standard wastewater treatment plants(effluent COD<20 mg·L^-1,Total Nitrogen（TN）<5 mg·L^-1,Total p Phosphorus（TP）<0.15 mg·L^-1)and ARGs,as well as the impact of various treatment processes on the diversity and abundance of ARGs in water;Understand the diversity and abundance of Mobile Genetic Elements（MGEs）in high standard wastewater treatment plants,and analyze the correlation between MGEs and ARGs;Understand the characteristics of bacterial community structure in high standard sewage treatment plants,clarify the relationship between bacterial community structure and ARGs,and provide a basis for optimizing sewage treatment processes and scientifically preventing and controlling ARGs pollution.The research results are as follows:（1）The distribution characteristics and removal efficiency of ARGs in sewage treatment plants:Based on the ARGs OAP analysis of pipelines,the relative abundance of ARGs in the wastewater along the sewage treatment plant was standardized and quantified.The results are as follows:a total of 26 ARGs types and 18 core ARGs types were detected in high standard sewage treatment plants,with 1081 ARGs subtypes present.In winter,the number of core ARGs subtypes（87）in sewage treatment plants was less than in summer（160）,The number of core ARGs subtypes shared between the two seasons is 72.Explanation:Similar to conventional sewage treatment plants,high standard sewage treatment plants are important environmental reservoirs for ARGs;High standard sewage treatment plants cannot effectively reduce the diversity of ARGs types in wastewater.The removal efficiency of ARGs varies greatly among different treatment units.The modified sequencing batch reactor（MSBR）unit（0.52 log）and membrane bio reactor（MBR）unit（0.28 log）have better removal efficiency of ARGs than other units（no more than 0.2 log）,but lower than the removal efficiency of the same process in other studies（2 log～7.1 log）;From the stability of ARGs removal efficiency,compared with biological treatment units,the removal efficiency of ARGs by two chemical treatment units,ozone contact tank and chlorination disinfection tank,is less affected by seasonal changes.（2）Distribution characteristics of MGEs in WWTP and their correlation with ARGs.In sewage treatment plants,a total of 1117～1180 insertion sequences（IS）,10 types of integrons,and 398～403 types of integrated and conjugative elements（ICEs）were identified.The correlation analysis results showed that in summer,there was a significant positive correlation between ICEs and ARGs in sewage treatment plants（P<0.05）,with 25 main ARGs having a significant positive correlation with at least 2 ICEs（P<0.05）.（3）Proteobacteria is the phylum with the highest relative abundance in sewage treatment plants,followed by Bacteroidetes and Actinobacteria.The biological treatment units such as MSBR,MBR and denitrification filter have greatly changed the microbial community structure in the sewage of the sewage treatment plant;In the advanced treatment stage,except for the denitrification filter,the microbial community structure in the effluent of other advanced treatment units is similar.Tetracyclines,MLS,polymyxin,β-lactams,chloramphenicol and aminoglycoside ARGs was significant correlation with bacterial community structure（P<0.05）.Bacteria within the phyla of Acidobacteria,Chloroflex,Bacteroidetes,and Firmicutes can carry multiple types of ARGs and have a relatively high abundance in sewage treatment plants,making them important potential antibiotic resistant bacteria（ARB）;The Dechromonas has a significant positive correlation with three major ARGs subtypes（sul1,ugd,and qac Edelta1）and is a potential ARB genus in sewage treatment plants.After advanced treatment,the relative abundance of pathogenic bacteria decreased,but the effluent still contains pathogenic bacteria.Escherichia and Streptococcus may be the main pathogenic ARBs in sewage treatment plants.