Heterologous expression of the tetracycline resistance gene tetX to enhance degradability and safety in doxycycline degradation.

Microbial remediation has the potential to inexpensively yet effectively decontaminate and restore contaminated environments, but the virulence of pathogens and risk of resistance gene transmission by microorganisms during antibiotic removal often limit its implementation. Here, a cloned tetX gene with clear evolutionary history was expressed to explore doxycycline (DOX) degradation and resistance variation during the degradation process. Phylogenetic analysis of tetX genes showed high similarity with those of pathogenic bacteria, such as Riemerella sp. and Acinetobacter sp. Successful tetX expression was performed in Escherichia coli and confirmed by SDS-PAGE and Western blot. Our results showed that 95.0 ± 1.0% of the DOX (50 mg/L) was degraded by the recombinant strain (ETD-1 with tetX) within 48 h, which was significantly higher than that for the control (38.9 ± 8.7%) and the empty plasmid bacteria (8.8 ± 5.1%) (P < 0.05). The tetX gene products in ETD-1 cell extracts also exhibited an efficient DOX degradation ability, with a degradation rate of 80.5 ± 1.2% at 168 h. Furthermore, there was no significant proliferation of the tetX resistance gene during DOX degradation (P > 0.05). The efficient and safe DOX-degrading capacity of the recombinant strain ETD-1 makes it valuable and promising for antibiotic removal in the environment.