Study On Diversity Of Antibiotics And Resistance Genes In Typical Tributary Sediments From The Three Gorges Reservoir

Overuse of antibiotics has accelerated the generation and transmission of antibiotic resistance genes?ARGs?in natural environment,which has great harm to the ecological environment.Exploring antibiotics and resistance genes in different watersheds has become a research hotspot in the field of environment.The Three Gorges Reservoir has the characteristics of a typical river-type reservoir,and its operation mode of"winter storage and summer drainage"has caused great changes in the water environment.Influenced by the backwatering effect in the reservoir area,many tributaries become sinks of land-based pollutants and have adverse effects on aquatic ecosystems.In order to investigate the pollution status of new pollutants in typical tributaries of the Three Gorges Reservoir,the sediments of Changshou Lake in the lower reaches of Longxi River,Ganjing River and Longtan River in the Zhongxian section of the three gorges reservoir area were studied in this study.The regional distribution characteristics of antibiotics and resistance genes and environmental impact factors were also investigated.The main findings are as follows:Residual concentrations of 14 antibiotics in five major categories of sulfonamides,tetracyclines,quinolones,macrolides and?-lactams were determined by liquid chromatography-mass spectrometry?LC-MS?.The results showed that the antibiotics in the sediments downstream of the tributaries of the Three Gorges Reservoir had obvious spatial heterogeneity.The average content of antibiotics in the sediments of Changshou Lake was 58.99 ng/g,which was generally expressed as the ecological farming area>ecotourism area>wetland protection area as a whole.The average antibiotic content of the Ganjing River and Longtan River sediments was 47.48 ng/g and 45.38 ng/g,respectively.At the same time,the risk quotient was used to evaluate the ecological risk of antibiotic residues in sediments.The results showed that the environmental risks of tetracycline and sulfamethoxazole in sediments were relatively high.Trimethoprim,ofloxacin and roxithromycin were expressed as trace residues,and the risk quotient is basically below 0.1.Other antibiotics were showing the medium risk.Spatially,the risk of antibiotics at each sampling point was significantly different.The average risk of Changshou Lake is 0.66,of which the individual points showing high risk.The average risk of Ganjing River is 0.49,and the average risk of Longtan River is 0.43,all of which are moderate risks,indicating that the ecological risk generated by antibiotics in sediments is not significant.Tetracycline resistance genes?tetA,tetB,tetC,tetG,tetM,tetO,tetQ,tetW?,sulfonamide resistance genes?sul1,sul2?,quinolone resistance genes?qnrA,qnrB,qnrC,qnrS?,macrolide resistance genes?ermA,ermB,ermF?,?-lactams resistance genes(bla _TEM,bla _SHV,bla_CTX-M),transposon?intI1,int2,Tn916f/1545r?,and 16S rRNA were determined by common polymerase chain reaction?PCR?and quantitative real-time PCR?qPCR?techniques.The results showed that?-lactam resistance genes and transposons were not detected in this study.The relative abundances of the other resistance genes were as follows:sulfonamides>tetracyclines>macrolides>quinolones.The average relative abundance of the resistance genes in the sediments of Changshou Lake was 6.34×10^-3.The distribution of ARGs at different sites was significantly different,showing that the content of resistance genes in eco-aquaculture areas was higher than that in eco-tourism areas,and the content in the wetland reserve was the lowest.The average relative abundance of the resistance genes of Ganjing River and Longtan River were 6.38×10^-3 and 6.07×10^-3,respectively.The similarity of exogenous input made the distribution of resistance genes more consistent.The distribution of antibiotics and resistance genes in the open natural environment is affected by many factors.Redundancy analysis and Pearson analysis showed that the amount ofantibiotics in the sediment was related to Ni,but the environmental impact factors of the new pollutants in different basins are significantly different.Except for the combined pollution of heavy metals?Mn,Zn,Cu,Pb?and antibiotics in Changshou Lake,there is also a significant correlation between antibiotics and organic matter.The antibiotics in Ganjing River are only significantly related to NO₂^--N.Longtan River has nothing to do with the environmental factors detected in this study,but does not rule out the interference of other environmental factors.The environmental impact factors of ARGs abundance in Changshou Lake are Mn,Zn,Ni and organic matter.The resistance genes of other watersheds are not affected by the environmental factors detected in this study.Correlation analysis between antibiotics and resistance genes indicates that antibiotics can induce the generation and spread of resistance genes.The results of homology analysis indicated that,in addition to homology between the same types of ARGs,different types of ARGs also have the same compound pollution sources.It may be that the same genetic elements cause ARGs to be linked,which makes the pollution sources of different ARGs have similarities.