The Mechanisms of Tetracycline in Shaping Antibiotic Resistance Gene Dynamics in Earthworm Casts During Vermicomposting

Earthworm gut digestion plays a crucial role in reducing antibiotic resistance genes (ARGs) during vermicomposting, offering significant potential for controlling ARG dissemination in livestock manure. However, the impact of residual tetracycline antibiotics on this process remains poorly understood. Herein, this study systematically evaluated the impact of tetracycline of three concentrations (0, 10, and 100 mg/kg) on ARG dynamics and microbial community evolution during 35-day vermicomposting of cattle manure. The results demonstrated that earthworm intestinal digestion effectively eliminated over 96% of initial ARG load in raw manure. Noticeably, tetracycline stress significantly enhanced total ARG abundance in the casts (<i>p</i> < 0.05), with distinct response patterns observed among different ARG types. Mechanistic analysis revealed that tetracycline potentially enhanced ARG persistence through two pathways: (1) promoting horizontal transfer via mobile genetic elements, and (2) altering gut microbial succession patterns that influence ARG host-microbe relationships. These discoveries contribute to our comprehension of antibiotic interference in vermi-remediation processes and provide insights for optimizing ARG mitigation strategies in contaminated livestock manure.