Distribution And Fate Of Pathogens And Virulence Factors In Municipal Water Supply And Drainage System

Municipal water pollution has been regarded as an environmental issue all over the world.Some water environments in urban area were polluted by the wastewater from industrial production and human activities,which contain diverse biological contaminants such as pathogens,antibiotic resistance genes(ARGs)and virulence factors(VFs).The polluted water carrying biological contaminants were delivered to the wastewater treatment plants(WWTPs)or discharged into water environments directly.The biological contaminants in the treated and untreated waste discharged into the receiving water could easily enter the drinking water treatment and pipe network system,posing a huge threat on the human health and ecological safety.In this study,samples were collected from WWTPs,receiving river,drinking water treatment plant and drinking water transportation and distribution system regularly.Polymerase chain reaction(PCR),quantitative real-time PCR(qPCR),454 pyrosequencing based on 16S rRNA genes and metagenomic sequencing were then simultaneously employed to characterize the microbial structures in the key nodes of municipal supply and drainage systems.The study characterized the fates of the human pathogenic bacteria and virulence factors during the wastewater treatment,and investigated the effects of the discharged effuent from WWTP on the bacterial community composition as well as biological contaminants of the receiving river.Besides,the study also revealed the changing pattern of bacterial communities and the mechanism of the removal of VFs in drinking water treatment system.The detailed results of this study are listed as follows:(1)Pyrosequencing and metagenomic sequencing consistently demonstrated that municipal sewage acts as an important source of human pathogenic bacteria,in which Arcobacter genus had the highest abundance,accounting for over 43.42%of total abundance of human pathogens in the WWTP.At species level,potential pathogens Arcobacter butzleri,Aeromonas hydrophila and Klebsiella pneumonia dominated in WWTP,which was also confirmed by qPCR.(2)Oxidation ditch,sand filter and anaerobic-anoxic-oxic(A2/O)process could remove 98.38%,98.52%and 74.17%of human pathogenic bacteria in sewage respectively.However,the presence of A.butzleri in the final effluent still deserves more concerns.(3)Considering the characteristics of the microbial community and biological contaminants in the WWTP and its receiving river,the WWTP investigated in this study had good removal efficiency on human pathogenic bacteria and ARGs.The effluent from the WWTP had no significant effects on the bacterial communities of downstream at phylum and 97%OTU(operational taxonomic unit)level.The increase of human pathogenic bacteria and ARGs at effluent outfall was observed,indicating that the WWTP effluent may play a role in the dissemination of biological contaminants into the receiving river.(4)454 pyrosequencing revealed high bacterial diversity in the drinking water(441-586 OTUs).Bacterial diversity decreased after chlorine disinfection,but increased after distribution through pipelines.Several types of human pathogenic bacteria were present in the drinking water and Pseudomonas aeruginosa had the highest abundance(over 1.1%of total sequencing reads).Most pathogens disappeared after chlorine disinfection,but Pseudomonas aeruginosa and Leptospira interrogans could still be detected in the tap water.(5)The result of metagenomic sequencing revealed the prevalence of various pathogenicity islands and virulence proteins in the drinking water,and translocases,transposons,Clp proteases and flagellar motor switch proteins were the predominant VFs.Both diversity and abundance of the detectable VFs increased after the chlorination,and decreased after the pipeline distribution.In conclusion,this study investigated the overall composition and change of microbial community and biological contaminants(human pathogenic bacteria,ARGs and VFs)in the key nodes of municipal water supply and drainage system,including sewage,WWTP,receiving water,drinking water treatment plant and drinking water distribution system by using high-throughput DNA sequencing-based metagenomic approaches.Overall,the findings of this study may improve our understanding on relationships between microbial community and biological contamination in urban areas and provide basic information for prevention of biological pollution.