Distribution Of Antibiotic Resistance Genes And Their Potential Hosts In Drinking Water Supply System

Antibiotic resistance has been considered as one of the greatest threats to human health and raised global concern.Antibiotic resistant bacteria(ARB)and genes(ARGs)are important carriers of antibiotic resistance.Drinking water safety is vital to human health.Therefore,it is necessary to investigate the distribution,variation and potential hosts of ARGs in drinking water supply systems.This research aims to systematically investigate the distribution of ARGs in the drinking water supply systems,to analyse the factors affecting the abundance of ARGs in river water and to investigate the removal efficiency of ARGs by the main treatment processes.By using metagenomic assembly and binning,this study intends to evaluate the risk characteristics of ARGs in the tap water at the user end and analyze the distribution of ARGs and their hosts in the tap water.This research designed a simulation experiemnt to investigate the effect of disinfection type,disinfectant concentration,and pipe material on the abundance of ARGs,microbial communities and ARG hosts in water and biofilm.The main conclusions of this research are as follows:Water samples of four seasons were collected from two drinking water treatment systems(from river water to tap water)in Jiaxing,China,and the abundance of 16 S r RNA gene,int I1 and 11 ARGs were quantified by q PCR.The results showed that the abundance of sulfonamide ARGs was the highest,and the abundance of quinolone ARGs was the lowest.Temperature was the main factor affecting the biomass and ARGs abundance in the system.As for the removal efficiency,wetland had no significant effect on the decrease of ARGs abundance,and ozone and chlorination were the most effective processes in the drinking water treatment plant to the reduction of ARGs and 16 S r RNA gene about three orders of magnitude reduction for each.After being transported by the pipeline,the abundance of 16 S r RNA gene in the tap water from two systems increased,while the total abundance of ARGs changed inconsistently.The simulation experiment of the drinking water pipe network was established by taking the tap water as the raw water.q PCR and high-throughput sequencing were used to study the changes of total biomass,target ARGs and microbial community structure during the operation of the simulated pipe network.The effects of pipe materials(steel pipe and Polypropylene-Random(PPR)pipe)and disinfectants(disinfectant-free,chlorination and chloramine group)on the effectes of ARGs and their potential host bacteria were incestigated.During the whole disinfection experiment,the total biomass showed a slow increase trend for the control group,and a similar trend for the chlorination and chloramine disinfection groups which increased first,then decreased after adding disinfectant,and then the biomass increased again.As for the pipe material effect,the total biomass was significantly higher in the steel pipe than that in the PPR pipe.Overall,the change of the abundance of ARGs and total biomass showed similar trends.The microbial community structure showed difference by chlorination and chloramine disinfection when the relative proportions of Firmicutes and Bacteroidetes decreased after chloramine disinfection.By metagenomic sequencing analysis,the effects of pipe material and disinfectants on ARGs abundance and the changes of their hosts were investigated in the simulated pipeline biofilm.A total of 99 ARGs subtypes were detected in the biofilm,conferring resistance to 16 ARGs types.Among which the four most abundant ARG types were multidrug,aminoglycoside,fosfomycin and bacitracin resistance genes.The total abundance of ARGs in the steel pipe was significantly higher than that in the PPR pipe,and the pipe material was the main factor affecting the abundance of ARGs in the simulated pipe biofilm,while the effect of disinfectants on the change of ARGs was not significant.The abundance of metal resistance genes(MRGs)in the biofilm of steel pipe was significantly higher than that of PPR pipe.Further analysis demonstrated that ARGs and MRGs promote antibiotic resistance in biofilms through a synergistic resistance mechanism.The hosts of ARGs mainly come from the phylum Proteobacteria,Actinobacteria and Planctomycetes.By using metagenomic assembly and binning methods,the composition and distribution of antibiotic resistome and their hosts in tap water along distribution pipeline from the same DWTP were explored.Multidrug,aminoglycoside and bacitracin resistance genes were the three most abundant ARGs types,among which omp R and bac A were the most abundant ARGs subtypes.The coexistence of ARGs on the same contig increased the risk of antibiotic resistance.The coexistence of multidrug resistance genes was the most common and the most typical is the formation of mdt CMux B cluster.Among the contigs carrying ARGs,10% were found to carry mobile genetic elements(MGEs),increasing the migration ability of ARGs.Genome binning reconstructed 203 high-quality metagenomic assembly genomes(MAGs),and indicated that more than half of the reconstructed genomes harbored multiple ARGs that exhibited multidrug resistance,for example,hosts from the family Burkholderiaceae exhibiting resistance to aminoglycosides,bacitracin,and multidrug resistance.Moreover,three multidrug-resistant opportunistic pathogens including Aeromonas,Tatlockia,Mycobacterium,Legionella and Sphingomonaswere identified in drinking water.This study provided basic data for ARGs and theoretical guidance for the reduction of ARGs in drinking water,and it has important scientific significance for controlling the risk of ARGs transmission in the water supply system.