Effects Of Human Activities On Microbial Communities And Antibiotic Resistance Genes In Sediment Of Jialing River

Rivers are the main source of human available water resources,and their water quality is closely related to human health.In recent years,as a large number of pollutants generated by human activities have flowed into rivers,they have affected the physical and chemical properties of river water bodies,and further affected the microbial community structure and resistance gene distribution in river water bodies.This study selected the Jialing River in the upper reaches of the Yangtze River as the research object,and explored the effects of different human activities on the microbial diversity,flora structure,and the abundance and distribution of tetracyclic resistance genes in the sediments of different watersheds.It also revealed the correlation between sediment microbial flora and tetracyclic resistance genes and sediment environmental factors.The main results are as follows,(1)Different human activities in rural and urban areas lead to different distribution characteristics of nitrogen pollutants and tetracyclic resistance genes in the sediments of the Jialing River.The concentration of nitrogen(ammonium nitrogen and nitrate nitrogen)in the sediments of the urban section in the lower reaches of the Jialing River is significantly higher than that in the upstream rural section(P<0.05).The economic construction and urbanization process of the urban section have contributed a lot to the pollution of ammonium nitrogen and other pollution in this section.The farming activities in the rural areas and the sewage activities in the cities are important reasons that cause the widespread existence of tetracyclic resistance genes and family mobile genetic elements.(2)Different human activities have a great impact on the microbial community in the sediments of the Jialing River,leading to differences in the composition of the microbial communities in the sediments of the Jialing River in different sections.The dominant categories in the rural section are Proteobacteria,Chloroflexi,Verrucomicrobia,and Bacteroidetes.The urban section is mainly composed of Proteobacteria,Chloroflexi,and Acidobacteria.The dominant bacteria in the rural section are Arenimonas,Dechloromonas,Flabacterium,and the urban section is mainly Nitrospira,Anaeromyxobacter and Geobacter.The structure of the bacterial flora in the rural section differs greatly between different small watersheds,while the urban section is relatively similar.The functional flora in the rural section contains a large number of denitrifying bacteria,including Luteolibacter,Rhodobacter,Arenimonas and Hydrogenophaga,while the urban section contains a large number of nitrifying bacteria Nitrospira and iron-reducing bacteria Anaeromyxobacter,Geobacter and denitrifying bacteria Thiobacillus.(3)A total of 30 tetracyclic resistance genes and 12 mobile genetic elements(MGEs)were detected in the sediments of the Jialing River.There is a significant relationship between tetracyclic resistance genes and mobile genetic elements(r=0.955,P<0.01),and human activities will affect the horizontal genes transfer in the sediments of the Jialing River.In addition,the mechanism of efflux pump and ribosome protection are the main resistance mechanisms of bacteria in the sediments of the Jialing River to tetracyclic antibiotics.The upstream water source(A1,A7)in the rural section contains fewer types and lower abundance of tetracyclic resistance genes and MGEs,and the tetracyclic resistance genes in the farm area(A5,A6)are dominated by tet G-02,tet A-02,tet M-01,and tet R-02,and are positively correlated with the dominant bacteria in the area,Flavobacterium and Arenimonas.The tetracyclic resistance genes in the sewage outfalls(C1,C4)of the urban section are mainly dominated by tet S,tet D-01,tet PA,and tet Q,and are positively correlated with the dominant genus Nitrospira in this area.(4)Through the correlation analysis of environmental factors,it is found that p H,NH₄⁺-N,TN,and TP are important environmental factors that affect the microbial diversity,community structure,and the distribution of tetracyclic resistance genes and mobile genetic elements in various small watershedindifferentsections,anditalso have an important impacton the type and abundance of microorganisms and resistance genes.The research results of this paper can provide certain guidance for the environmental governance of river ecosystems and water environmental risk assessment,but the control mechanism of nitrogen pollution in the river system and the removal mechanism of tetracycline resistance genes need to be further studied.