Enhanced removal of ciprofloxacin and reduction of antibiotic resistance genes by earthworm Metaphire vulgaris in soil.

Antibiotic residues could promote the dissemination of antibiotic resistance genes (ARGs) in the environments, and biodegradation represent a major route for antibiotic removal. Previous studies have showed that earthworm could enhance the degradation of certain organic contaminants, however, its effectiveness in ciprofloxacin removal and ARG reduction in soil remains unclear. In the present study, high-performance liquid chromatography, 16S rRNA gene sequencing and high-throughput quantitative PCR were employed to explore the effects of earthworm addition on ciprofloxacin removal and ARG abundance in ciprofloxacin-amended soil. Ciprofloxacin removal was significantly higher in earthworm cast as compare to control soil, and ARG abundance in earthworm cast was significantly lower than that of control soil. Procrustes analysis together with Mantel test showed that the ARG profiles were strongly associated with bacterial communities, indicating that the lower abundance of ARGs in cast samples could be attributed to changes in bacterial community compositions by earthworm activity. Flavobacterium and Turicibacter were enriched in cast samples, which were negatively correlated with ciprofloxacin concentration (p < 0.05), implying their potential roles in ciprofloxacin removal. These results suggested that earthworm gut is a hotspot for ciprofloxacin removal, and could be an option for mitigation of antibiotic pollution in soil.

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Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.