| In recent years,the extensive use of antibiotics has caused the contamination of both antibiotics and antibiotic resistance genes(ARGs)in the environment.In this study,antibiotics,ARGs and Class 1 integron gene(intI1)in the water,soil and sediment of the Three Gorges reservoir were characterized.Thirteen antibiotics(OTC,TC,CTC,STZ,SDZ,ST,SMZ,TMP,ENR,OFL,NOR,DXC,CIP)were quantified by HPLC,while sixteen target genes(3 sul genes:sul1 sul2,sul3;8 tet genes:tetA,tetB,tetC,tetM,tetO,tetQ,tetW,tetG;4 qnr genes:qnrA,qnrB,qnrD,qnrS;intI1)were analyzed by real time quantitive PCR(qPCR).The analysis for concentration and distribution of antibiotics and ARGs were conducted as well as the potential environmental factors,such as TOC and pH.Redundancy analysis was also used for exploring the relationship between antibiotics and related genes.Ten(OTC,TC,CTC,STZ,SDZ,ST,SMZ,TMP,ENR,OFL)of target antibiotics was detected in all samples with 100%frequency,while CIP was not found in this study.The NOR and DXC were below 50%in soil and sediment,and they were not detected in water.The results indicated that the Three Gorges reservoir was polluted by various antibiotics.The highest average concentrations were found for TPM(119.1 ng/L),ENR(43.2 ng/g)and ENR(42.6 ng/g)in water,soil and sediment respectively.The highest concentration ranged from 27.ng/L to 359.2 ng/L of SDZ in water,1.7ng/g to 154.1ng/g of ENR in soil and 10.8ng/g to 121.3ng/g of ENR in sediment,respectively.Pearson correlation analysis showed that the total concentrations of tetracycline had negative correlation between water and sediment,and the concentration of SDZ and ST had positive relationship between water and soil respectively,indicating these antibiotics had dynamic exchange and partition equilibrium in different matrixes.In addition,the STZ had positive correlation with TOC and pH in water.Hence,TOC and pH may be the important factors influencing the distribution of STZ in the water of Three Gorges reservoir.Conventional PCR revealed that the sull,sul2,tetA,tetB,tetM,tetQ,tetG and intI1 had 100%frequency,while tetW was not found in all samples.For sul group,sul1 and sul2 had higher detection frequency than sul3 in three matrixes.For tet group,the efflux pump genes(tetA,tetB,tetC,tetG)were more detected than ribosomal protection protein genes(tetM,tetO,tetQ,tetW).Among all target genes,sul1 was most widely distributed,with average abundance 2.2×10-1 copies/16S-rRNA,1.1×10-1 copies/16S-rRNA and 6.4×10-2 copies/16S-rRNA in water,soil and sediment respectively.In group of five tet genes(tetA,tetB,tetC,tetG,tetM),the average concentrations of tet A was highest(1.0× 10-2 copies/16S-rRNA)in water and the order was tetA>tetC>tetG>tetQ>tetB>tetM.In soil and sediment,tetB was more abundant among tet group with 1.1×10-2 copies/16S-rRNA and 3.3×10-3 copies/16S-rRNA,respectively.Furthermore,intl1 had positive correlation with various ARGs,indicating it may contribute the horizontal gene transfer among bacterium.And the composition difference of ARGs in sites may be associated with the regional drug characteristics and types.Correlation analysis also showed that efflux pumps had positive relation with ribosomal protection proteins within each matrix,while only tetM exbited relevance between soil and sediment among three matrixes.The distribution of antibiotic and ARGs in the Three Gorges reservoir mainly affected by human activity.The concentrations were generally higher near the hospitals,livestock farm and WWTP,suggesting these areas could be the important reservoir for antibiotics and ARGs.The redundancy analysis also showed the relationship between antibiotics and ARGs.The percentage of variance explained by the first two axes was 80.96%,74.29%,85.37%in water,soil and sediment respectively.And sampling sites in each matrix were clustered in three groups,indicating there locations had resembling contamination profiles of related genes.Some antibiotics had positive correlation with corresponding ARGs,which may be one of the important environmental factors. |
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