| Since the invention of antibiotics,they have been widely used in human medical treatment and livestock disease control and growth promotion,but the environmental bacterial resistance caused by the massive and unreasonable use of antibiotics has become a global concern,and studies have shown that river ecosystems are the main accumulation sites of antibiotics and resistance genes.As an ecological barrier in the upper reaches of the Yangtze River and an important habitat for rare aquatic organisms,the water quality and water ecology of the Chishui River are not only related to the local socioeconomic development,but also have an impact on the water environmental safety in the middle and lower reaches of the Yangtze River.Therefore,in this study,water bodies and sediment samples from the Chishui River were collected in April(dry season)and August(wet season)in 2021,and the spatial and temporal distribution characteristics and sources of 21 antibiotics in four categories and 11 antibiotic resistance-related genes in the Chishui River were studied by solid-phase extraction-liquid chromatography-mass spectrometry and fluorescence PCR,and analyzed by high-throughput sequencing technology The spatial distribution of microbial communities in the samples was analyzed by high-throughput sequencing technology,and on this basis,correlation analysis was used to explore the main factors affecting the distribution of ARGs in the environment,aiming to provide theoretical support for the prevention and control of antibiotics and resistance gene pollution of water bodies in the Chishui River basin,and the main research results obtained are as follows.(1)Spatial and temporal distribution characteristics and source analysis of antibiotics in the Chishui RiverThe concentrations of four types of antibiotics in surface water and sediment of the main stream of Chishui River were ng/L and ng/g,and the detected species and concentration levels were greater in the dry season than in the wet season.Sulfadiazine,sulfamethoxazole,sulfamonomethoxypyrimidine,sulfamonomethoxypyrimidine and ofloxacin were the main types of detection,with the highest concentration of of ofloxacin(170.26 ng/L).In terms of spatial distribution,the average antibiotic levels were higher in the upstream section of surface water than in the middle and downstream sections,.The total antibiotic concentrations in dry and abundant water sediments ranged from 10.51 to 434.69 ng/g and 9.85 to 83.77 ng/g in dry and wet season respectively,and the highest average concentrations of antibiotics were chlorotetracycline(16.97 ng/g)and ofloxacin(6.08ng/g)in sediment samples in the two seasons,respectively,in the downstream section of the Wuma River confluence S10(437.46 ng/g)and S2(54.62 ng/g)upstream of the Little River confluence,respectively,and there was some increase in antibiotic concentrations downstream of the confluence in surface water tributaries.The principal component-multiple linear regression analysis indicated that livestock and poultry farming was the main source of antibiotic pollution in surface water,and its source contribution was 45.94%and 42.47%in the dry and abundant water periods,respectively.(2)Characteristics of antibiotic resistance gene assignment in Chishui RiverNine types of ARGs and two types of integrons were detected in the surface water samples of the dry river during the dry period,and the absolute abundance ranged from 1.53×10~6to 1.41×10~8copies/L.Only tet B was not detected during the wet season,and the absolute abundance of ARGs ranged from 3.62×10~4to 1.26×10~8copies/L.sul3 and tet A were the main types of ARGs detected in the surface water of both seasons.The absolute abundance of ARGs in tributaries was higher than that in main streams.Eleven antibiotic-related genes were detected in sediments during both the dry and wet seasons,and the ARGs with the highest mean absolute abundance were erm B(1.96×10~6copies/g)and sul3(1.74×10~6copies/g),respectively.The higher contents of ARGs in surface water and sediment were all in the midstream section.pearson analysis showed no correlation between most antibiotics and ARGs except LIN and SMM,while there were significant correlations between intl1 and heavy metals and ARGs.(3)Spatial and temporal distribution characteristics of microbial communitiesSurface water samples in both seasons had Proteobacteria as the microorganisms with the highest detected abundance at the phylum classification level,with the average relative abundance in the dry season(60.26%)higher than that in the wet season(39.89%),and the phylum with the highest detected abundance specific to the wet season were Deinococcus-Thermus,Acidobacteria Chlamydiae and Candidatus＿Saccharibacteria,and seasonal changes had a significant effect on the distribution of dominant microbial communities in surface waters.Phylum Chloroflexi and Nitrospirae were unique to sediments compared to surface water,but Proteobacteria still had the highest detected abundance.In addition,the relative abundance of the dominant microbial community in the sediment decreased to some extent at the tributary confluence.(4)Correlation of microbial communities with antibiotic resistance genesMost microorganisms in surface water except LIN basically showed negative correlation with antibiotics,and the microbial species with correlation with antibiotics in sediment environment were higher than those in surface water,among which the strongest significant correlation was found between Verrucomicrobia and SMZ(P<0.001,R=0.67).Based on the results of the correlation analysis between microorganisms and ARGs,it is clear that one microorganism may be correlated with multiple ARGs,and multiple potential host microorganisms may co-exist in the same ARGs. |
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