Dual roles of tetracycline-degrading bacteria in pollutant detoxification and resistome reshaping under tetracycline-copper co-contamination.

Combined contamination of soils with antibiotics and heavy metals represents a growing environmental challenge, yet remediation strategies addressing their synergistic toxicity remain limited. In this study, the bioremediation potential of a tetracycline-degrading bacterial consortium (Raoultella sp. XY-1 and Pandoraea sp. XY-2) was evaluated in tetracycline-copper (TC-Cu) co-contaminated soils by integrating chemical, biological, and ecological assessments. Soil column experiments demonstrated that bioaugmentation significantly enhanced TC degradation (48.57-53.71% after 90 days) compared to uninoculated controls (<12%), while simultaneously reducing copper bioavailability by shifting acid-extractable and reducible fractions toward more stable oxidizable forms. Inoculation further alleviated the strong inhibition of soil enzymatic activities (sucrase, urease, phosphatase), reflecting improved soil functional recovery. Metagenomic sequencing revealed that TC-Cu co-contamination reshaped microbial community composition, particularly increasing the relative abundance of Actinomycetota and Campylobacterota. Bioaugmentation further facilitated the establishment of Raoultella and indirectly stimulated indigenous resistant taxa through community interactions. Correlation network analysis further revealed that Raoultella was a highly connected genus in co-occurrence networks of antibiotic resistance gene (ARG)- and metal resistance gene (MRG)-hosting genera. LC-MS detection of intermediate products during TC microbial degradation proposed three microbial degradation pathways and inferred microbial resistance mechanisms under TC-Cu coexistence. Collectively, these findings highlight that TC-degrading bacteria not only reduce pollutant toxicity but also reshape microbial and genetic landscapes in co-contaminated soils, potentially suppressing the diffusion risk of resistance genes at low TC-Cu level. This work provides novel insights into the ecological trade-offs of bioremediation and supports the development of targeted, sustainable strategies for complex antibiotic-metal pollution scenarios.