Study On The Spread And Diffusion Of Bacteria And Antibiotic Resistance Genes In The Sewage Outlet

With population growth and the development of coastal cities,the massive discharge of sewage into the sea from sewage outlets has led to increasingly serious marine pollution.However,in the monitoring and evaluation standards of China’s sewage outlets and adjacent sea areas,chemical monitoring indicators are relatively complete,while microbiological indicators are less involved.The pathogenic microorganisms in the sewage into the sea’s sewage outlet affect the water quality of the adjacent seas and pose a huge threat to the health of humans and marine life.The abundance and community structure of microorganisms in the sewage outfall can not only reflect the characteristics of the sewage outfall habitat where the microorganisms are located,but also explain the function and role of microorganisms in the sewage ecosystem.In addition,sewage contains many antibiotic resistance genes(ARGs),which pose a threat to human health and public safety.Therefore,exploring the temporal and spatial distribution characteristics of bacteria and ARGs in sewage,transmission and diffusion mechanisms,and influencing factors are essential for effective water quality environmental monitoring and management.In this study,the sewage outlet of Dalian Xinghai Bathing Beach was used as the research area,and the seasonal temporal and spatial changes of the microbial diversity and community structure in the sewage into the sea and the adjacent sea area were analyzed,the propagation and diffusion law of four pathogenic bacteria in sewage in the process of discharging the sea was explored,and the propagation and diffusion model of E.coli at the sewage outlet into the sea was constructed,the occurrence characteristics of ARGs in different environmental media(seawater,biofilm)in the sewage outlet and adjacent sea areas were analyzed.The specific results are as follows:1.High-throughput sequencing technology was used to reveal the seasonal distribution differences of bacterial diversity and community structure in the Xinghai sewage outlet.Proteobacteria and Bacteroidetes were the main groups of bacteria in the sea area adjacent to the sewage outfall,and the dominant genera were Glaciecola and Marinobacterium.On the spatial scale,the bacterial diversity at the sewage outlet was the highest.Due to tidal and seawater dynamics,as the distance from the sewage outlet increased,the microbial diversity gradually decreased;On the time scale,the seasonal changes of microbial diversity and community structure were very obvious,with the highest microbial diversity in summer and the lowest in winter.And through q PCR experimental analysis,it can be known that the 16 S bacterial gene abundance in the sewage: autumn > summer >winter.2.Detected the abundance and distribution of E.coli,Enterococcus,Staphylococcus aureus and fecal coliforms in the sewage from the sewage outlet in summer,autumn and winter through traditional bacterial culture experiments.The four bacteria at the sewage outlet have the highest abundance.Among them,Staphylococcus aureus had the highest abundance and it was the least affected by the season.Seasonal changes had the most significant impact on the abundance of Enterococcus.Analysis of the correlation between bacterial abundance,environmental factors and microbial community structure found that in summer and winter,water temperature,electrical conductivity and dissolved oxygen will significantly affect the bacterial community structure,while in autumn,p H,redox potential and salt Degree is the main influencing factor.The microbial community structure has the highest correlation with E.coli(-0.76 <r <0.79),followed by Enterococcus(-0.88 <r <0.77)and fecal coliforms,and the lowest correlation with Staphylococcus aureus(-0.62 < r <0.63).3.By using HT-q PCR method,a total of 208 ARGs were detected from 219 target ARGs in the total biofilm DNA,extracellular DNA(e DNA),intracellular DNA(i DNA)of biofilm at the sewage outlet and the seawater DNA in the adjacent sea area.A total of 208 ARGs including aminoglycosides,β-lactams,chloramphenicol,sulfonamides,MLSB,tetracycline,vancomycin,etc.were detected.The main resistance mechanisms of ARGs in different media included antibiotic inactivation,cell protection,efflux pump and so on.The abundance of most types of ARGs in the total DNA of seawater at the sewage outlet were higher than the total DNA of biofilm.Further analysis showed that the abundance of different ARGs in e DNA were mostly higher than those of i DNA.The distribution of β-Lactamase in e DNA was significantly higher than other media.The abundance of ARGs in seawater had a significant correlation with physical and chemical factors and heavy metals.Among them,salinity,p H and conductivity had a significant negative correlation with the abundance of ARGs,Cu and Zn in heavy metals had a significant positive correlation.4.22 groups of E.coli abundance data were collected at 0m,50 m,100m,300 m,500m away from the sewage outlet in three seasons including summer,autumn and winter as preliminary data preparation,By calculating the initial conditions and boundary conditions,setting the calculation domain and water depth and other parameters,calculating the time step and other methods,the E.coli diffusion model was constructed.The results showed that the flow direction of the rising and falling tides was opposite.The flow direction was from east to west at high tide,and from west to east at low tide,but it had little effect on the tide of the study area,and the spread of E.coli abundance on different days of the same month were not same,the abundance in the seawater at the beginning of August was less,and the abundance of bacteria was higher at the end of August,and the phenomenon of bacteria spread was obvious.The result is in good agreement with the measured value.In summary,the Xinghai sewage outlet was the research area.The temporal and spatial distribution of microbial diversity and community structure in the sewage from the sewage outlet is greatly affected by the seasonal changes of environmental factors(such as temperature),and the distribution of ARGs in four different media including seawater and biofilm is significantly different.The spread and diffusion model predicts the temporal and spatial distribution of E.coli in sewage.A more complete understanding of the proliferation of microorganisms,the distribution of ARGs and potential ecological risks in the sewage from the sewage outlet provide a theoretical basis for the efficient management of sewage discharge.