| The application of livestock manure in farmland brought a large number of antibiotics and antibiotic resistance genes（ARGs）into the soil,making the soil an important sink for antibiotics and ARGs.Antibiotics and ARGs in soil could pose a significant threat to human health through the food chain.Earthworm is called“soil ecosystem engineer”,which plays an important role in bioremediation of soil organic pollution.Therefore,tetracycline antibiotic chlortetracycline（CTC）with large dosage and high detection rate was selected as the target pollutant;Metaphire guillelmi as well as Eisenia fetida were chosen as the experimental organisms,and a series of soil culture experiments were conducted in this study.Liquid chromatography-tandem mass spectrometry,high throughput sequencing,q PCR,a soil enzyme kit（microplate method）,redundancy and network analysis were used to investigate the effects of earthworms on the dynamics of CTC degradation and the abundance of ARGs in soil,analyze the changes of soil bacterial community,elucidate the relationships among CTC,ARGs and bacterial community as well as the improvement of earthworm on soil fertility under the selective pressure of CTC pollution.The impacts of earthworms on the accumulation and transportation of antibiotics and ARGs in soil and plant were further studied by pot experiment.The results of this study will provide theoretical support for remediation of antibiotic and ARGs pollution and improvement of the quality of antibiotic-contaminated soil by earthworm.The main results and findings are shown as below:（1）Both Metaphire guillelmi and Eisenia foetida could accelerate the degradation of CTC in soil,with the maximum increases of degradation rate were 9.83～28.88%;meanwhile,two earthworms also inhibited the amplification of ARGs and int I1 in soil,and their abundance decreased by 34.97～44.82%and 37.18～63.24%respectively.In addition,two earthworms could increase the degradation of CTC metabolites.（2）Earthworms promoted the growth of CTC degrading bacteria,such as Flavobacterium,Aeromona,luteolibacter,adhaeribacter as well as Pseudomonas and increased the abundance of CTC degrading genes,accelerating the degradation of CTC.The addition of two kinds of earthworms significantly changed the bacterial community structure in CTC-contaminated soil at the end of cultivation,and the effects of different kinds of earthworms were also distinct.The decline of the abundances of Actinobacteria,Acidobacteria,Gemmatimonadetes and CTC concentration were closely related to the decrease of abundances of ARGs.（3）The activities of dehydrogenase,catalase,urease and alkaline phosphatase in the soil were activated by CTC with maximum activation rates of 11.38～54.99%;the activity of catalase was inhibited by CTC with a maximum inhibition rate of 4.56%.After adding earthworm,the activities of dehydrogenase,catalase,invertase and urease in the soil were activated with maximum activation rates of 4.00～88.5%;the activity of alkaline phosphatase was inhibited by earthworms with a maximum inhibition rate of 23.77%～24.99%.Additionally,earthworms significantly reduced soil p H and organic matter content.The result of redundancy analysis showed that the soil CTC residual,bacterial community,p H and organic matter were the main factors affecting the change of soil enzyme activities.（4）Earthworms reduced the accumulation of CTC and the abundance of ARGs in soil,lettuce roots and leaves.By adding earthworms,the CTC residual were decreased by11.72～22.79%,15.71～36.10%and 8.93～19.64%;the abundances of ARGs were declined by22.38～26.96%,25.11～44.05%and 24.38～25.36%respectively in soil,lettuce roots and leaves with the initial CTC concentration of 50 mg·kg-1 in soil.The addition of earthworms resulted in the succession of the structure of bacterial community in soil,lettuce roots and leaves.The reduction of the abundances of ARGs in lettuce was related to the decline of the abundances Actinobacteria and Firmicutes. |
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