Investigation On The Distribution Profiles Of Pathogenic Bacteria And ARGs In Water Environment And Their Inactivation Mechanism Under Photocatalytic Stress

Human industrial activities produce large amounts of industrial waste water.Depending on the type of industry,the composition of the sewage is also different.However,it is indisputable that all the generated sewage will still be discharged into the surface water environment after being treated by the treatment process.In a water environment with complex composition,the selective pressure may force microorganisms in the water environment to evolve toward antibiotic resistance,resulting in more and more antibiotic resistance genes(ARGs)in the environment.There are also a wide variety of opportunistic pathogens that can cause disease in the water environment.A large number of ARGs that also exist in the water environment provide a strong support for the transfer of resistance from common bacteria to opportunistic pathogens,which may represent an important way for antibiotic resistance to cause human health risks.Therefore,it is a challenge of profound significance to fully understand how the ARGs in industrial wastewater grow in the receiving water or the possible health risks of pathogens gaining resistance.In order to control this health risk,it is necessary to explore how to efficiently kill pathogenic bacteria.For this purpose,after comprehensively comparing the advantages and disadvantages of conventional sterilization techniques such as chlorine,ultraviolet,and photocatalysis,we choose photocatalytic technology with low side effects as the sterilization method to explore its sterilization mechanism.Therefore,the main objectives of this thesis are:(1)To study the distribution of microbial communities in six types of water environments and the impact of environmental factors on microorganismsy;(2)To study the distribution characteristics of ARGs and pathogens in different types of industrial wastewater and rivers,and explore the possibility of antibiotic resistance being transmitted to pathogens and the harm it causes to human health;(3)To study the killing effect of photocatalytic technology on pathogens.The main research contents and results of this paper are as follows:(1)First,This study analyzes the current status of microbial distribution in water samples such as wastewater from food processing plants,wastewater from pig slaughterhouses,wastewater from traditional Chinese medicine pharmaceutical plants,hospital wastewater,wastewater from wastewater treatment plants,and river water.The bacterial domain is the most abundant domain among the six samples,and the Proteobacteria phylum is the most abundant phylum among the six samples.Although wastewater comes from different types of pollution-producing companies,the shared microbial species account for as much as 90%.Among the environmental factors(p H,TOC,COD,Cd,Pb)that were screened for less correlation,Cd and Pb were negatively correlated with the bacterial domain and Proteobacteria in each sample.Through principal component analysis,it was found that the microbial composition in river water was most similar to wastewater from food processing plants,and was the most different from wastewater treatment plants wastewater.(2)Furthermore,based on metagenomics analysis methods,the study of the distribution of antibiotic resistance genes and opportunistic pathogens in the water environment was carried out.The most abundant pathogens in the six water samples were Salmonella,Pseudomonas aeruginosa,Fusarium graminearum,Magnaporthe grisea,Staphylococcus aureus,and Klebsiella pneumoniae.Through non-metric multi-dimensional scale analysis,it was found that the composition of pathogenic bacteria in river water and pig slaughterhouse water samples were similar.At the same time,bacitracin resistance genes are the most abundant in samples from hospitals,slaughterhouses,sewage treatment plants,and rivers,accounting for more than 50%;Antibiotic resistance genes in samples from Chinese medicine pharmaceutical factories and food processing plants are relatively scattered,with a single antibiotic resistance gene accounting for no more than 30%;among them,the bacitracin resistance gene of bac A and the sulfonamide resistance gene of sul1 are the most abundant ARGs;the composition of ARGs in river water is most similar to slaughterhouse wastewater,hospital wastewater and wastewater treatment plant sewage.The Staphylococcus aureus,Streptococcus pneumoniae and Escherichia coli have co-occurrence with above 10 ARGs.The drug efflux pump mechanisms of ABC,RND and MFS transport protein abundance occupy the top three in the transport protein.The abundance of aggressive VFs in the six types of water samples is higher,and they have a strong correlation with potential pathogen hosts,suggesting a higher microbial risk..(3)Finally,in order to reduce the health risks caused by pathogens in the surface water environment,we have carried out research on the mechanism of killing pathogens.Combined with the previous research,the common opportunistic pathogens in the water environment were selected as the sterilization targets,so Escherichia coli,Staphylococcus aureus and Pseudomonas aeruginosa were selected.Compared with the other two bacteria,Escherichia coli has the best sterilization effect under photocatalytic sterilization.The active oxygen of Escherichia coli has a faster production rate and a larger total amount than Staphylococcus aureus and Pseudomonas aeruginosa,and the change trend of CAT enzyme activity of the three strains is roughly the same.Combining the bactericidal effect,ROSs and CAT enzyme activity,it can be seen that photocatalytic technology can stimulate Escherichia coli to produce more ROSs,destroy its oxidation/antioxidant system balance,and achieve a higher bactericidal effect.