Temporal And Spatial Distribution Characteristics Of Antibiotic Resistance Genes And Their Correlations With Environmental Factors In Sediments From The Yangtze Estuary And Adjacent Coastal Area

As a widely used drug,antibiotics are not only used in the human medical field,but also widely used in the prevention of livestock diseases.Antibiotics are released into the surrounding aquatic environment through point source pollution and non-point source pollution,causing antibiotic residues and accelerating the production and spread of antibiotic resistance genes(ARGs)in the aquatic environment.As a novel contaminant,ARGs are "replicable" and can transfer genes horizontally,for example,plasmid exchange to spread resistance genes.Therefore,the durability of the resistance gene in different environmental media is greatly increased.At the same time,the occurrence characteristics of ARGs in the environment are also affected by other environmental factors,such as heavy metals and p Hysical and chemical factors.Heavy metals have a certain impact on the migration and propagation of ARGs in the environment because of their high toxicity,many forms,easy accumulation and non-degradability.In this paper,the study selected the Yangtze River estuary and adjacent waters near the city with large scale,dense population and rapid economic development.A total of 175 sample sediments were collected in two seasons.UPLC-MS/MS was used to determine the five major classes of 20 antibiotics,using PCR and Q-PCR were used to quantify 8 kinds of ARGs.The total amount of heavy metals in the samples was determined by ICP-OES,and the acid extractable metals in the samples were determined by ICP-MS.At the same time,p Hysical and chemical indicators of sediments,including p Hysical and chemical indicators such as particle size,TOC,p H,temperature and depth,were also determined.Based on the detected data,the spatial and temporal distribution characteristics of ARGs were studied,and the correlation between ARGs and detected environmental factors was studied to provide theoretical support for the pollution prevention and control of environmental pollutants in the Yangtze River estuary and adjacent sea areas.The main research findings and understandings of this research include:(1)In the sediments of the Yangtze Estuary and adjacent coastal area,the average consentration of antibiotic resistance genes in summer showed: 16S-r RNA >aac(6')-Ib > tet A > tet W > int I > sul2 > sul1 > sul3.The average consentration of antibiotic resistance genes in summer showed: 16S-r RNA > sul2 >aac(6')-Ib > tet A > sul3> int I > tet W > sul1.In addition to sul2 and sul3,the other six antibiotic resistance genes average consentration in summer was higher than winter.(2)In summer,the high-value areas of sulfonamide resistance genes and quinolone resistance genes are concentrated in the adjacent waters of the Yellow Sea.In winter the high-value areas are concentrated to the south of Zhejiang and Fujian.The two-season high-value areas of the tetracycline resistance genes are concentrated in the adjacent waters of southern Zhejiang and Fujian.All the detected gene concentrations in the Yangtze River estuary and the extended waters outside the mouth were in the low-value area.(3)Sulfonamide resistance genes have significant differences in seasonal distribution.The relationship among sulfonamide resistance genes concentration in summer is sul2> sul1> sul3.The relationship of sulfonamide resistance gene concentration in winter is sul2> sul3> sul1.Sul2 has the highest contribution rate to sulfonamide resistance genes in the environment.The tetracycline resistance gene showed tet A > tet W in both seasons,which is consistent with the concentration distribution of tetracycline resistance genes in the inland rivers of Shanghai.(4)The seasonal differences in antibiotic concentration in the sediments of the Yangtze Estuary and adjacent coastal area were significant.In summer,the detection rates of five major antibiotics sulfa antibiotics,tetracycline antibiotics,fluoroquinolone antibiotics,macrolide antibiotics and chloramp Henicol antibiotics were 48.51%,0.09%,98.77%,40.74%,and 14.81%.In winter,these five types of antibiotics were detected only by sulfa antibiotics and fluoroquinolone antibiotics,with a detection rate of 11.54% and 100%.The highest detection rate of fluoroquinolone antibiotics ranged from 0-30.87 ng/g in summer,with an average content of 4.43 ng/g;in winter,the content of fluoroquinolone antibiotics ranged from 0 to 9.83 ng/g,and The average value was 5.45 ng/g.Fluoroquinolone antibiotics are ubiquitous in sediments and the pollution is more serious.This result is lower than the content of fluoroquinolone antibiotics in the sediments of the Yangtze River estuary,but its detection rate and content are dominant.(5)Most of the metal elements in the sediments of the Yangtze Estuary and adjacent coastal area showed a decreasing law in the east-west direction in summer,and the content in the nearshore was higher than that in the far-sea.The spatial distribution of most metal elements in winter shows the north-south direction,and the content of the adjacent sea area in the northern Jiangsu Yellow Sea is higher than that in the southern Zhejiang-Jiangxi sea area.The content of acid-exchangeable metals in the sediments of Yangtze Estuary and adjacent coastal area showed Mn > Zn > Ni > Cu > Pb > Cr > As > Cd.The spatial distribution of most acid-exchangeable metals content in summer is similar to that in the muddy area.(6)Correlation analysis was carried out among antibiotics,total metal concentration,acid-exchangeable metals and other environmental factors and concentration of ARGs.Antibiotics may not be the dominant factor regulating the occurrence of ARGs.There was a significant correlation between the total concentration of various metals and the abundance of ARGs.For 16 S r RNA,there was a significant correlation between the concentration of Fe and Cu,Ni,Pb and Cr in summer(P < 0.05).And the correlation coefficients are 0.237,0.400,0.337,0.238 and 0.332,respectively.For the tetracycline resistance gene,it was significantly correlated with Cu and Zn in summer and winter(P < 0.01).It is suggested that Cu and Zn may be the main metal elements that regulate the occurrence of tetracycline resistance genes.There was a significant correlation between acid-exchangeable Cu,Zn,Ni and the abundance of ARGs.acid-exchangeable Cu was significantly positively correlated with sul2,sul3,tet A and tet W(P < 0.01).In addition,the clay,silt and water temperature were significantly correlated with ARGs(P < 0.05),indicating that ARGs were present in the environment and regulated by environmental factors.