Differential mechanisms of two ecological earthworms promoting the degradation of doxycycline in soil

In recent years, doxycycline (DOX) has been frequently detected in agricultural soils, highlighting the need for effective remediation strategies. This study investigated the effects of two ecological earthworms ( Eisenia fetida and Metaphire guillelmi ) on DOX degradation in soil. By examining changes in soil microbial community, degradation-related genes and transformation products, the mechanism by which earthworms enhance DOX degradation were elucidated. Results indicated that both earthworms significantly promoted DOX degradation, with Metaphire guillelmi exhibiting greater efficacy. Compared to control, residual DOX concentrations in earthworm-treated soils decreased by 23.03%∼41.40% ( P < 0.05). The two species operated through distinct mechanisms: Eisenia fetida significantly promoted the proliferation of the degradation gene tetX . Bacterial genera such as Lysobacter , Mycobacterium and Adhaeribacter were potential host bacteria for tetX . These tetX -carrying bacterial genera showed marked proliferation in earthworm treatments, thus facilitating the degradation of DOX. Whereas, Metaphire guillelmi primarily altered soil microbial interspecific relationships, promoted the mutualistic cooperation of the whole soil microbial community including the potential degrading bacteria such as Lysobacter , norank_f_ TRA3-20 and MND1 , thereby exerting more powerful promoting effects on DOX degradation. E. fetida primarily promoted oxidation/reduction, demethylation and structural rearrangement of DOX, whereas M. guillelmi induced a distinct transformation pathway characterized by the formation of a cysteinylglycine conjugate. Moreover, while DOX stimulated the proliferation of most tetracycline resistance genes (TRGs) and mobile genetic elements, both earthworms inhibited the proliferation of plasmids and most TRGs but promoted the proliferation of insertion sequences. This study provides theoretical support for developing earthworm-based remediation technologies for antibiotic-contaminated soils.