Screening and identification of an oxytetracycline degradation strain resistant to Cu²⁺ and Zn²⁺ and its characteristics

Objective  As the main feed additive in breeding industry, Cu²⁺, Zn²⁺ and oxytetracycline contribute to high amounts of residues in livestock and poultry excrement and sewage, forming complex pollution. We are aimed at screening strains to degrade oxytetracycline under the stress of Cu²⁺ and Zn²⁺.

Method  The strain DJ1 of oxytetracycline degrading bacteria was screened and isolated from culture wastewater using selective medium. The biodegrading conditions of oxytetracycline by strain DJ1 were optimized. The tolerances of strain DJ1 to other tetracycline antibiotics and chloramphenicol were determined.

Result  The strain DJ1 was identified as Cutaneotrichosporon cutaneum based on morphology and 18S rDNA sequence alignment. The oxytetracycline degradation rate of DJ1 reached 78.83% after five days of culturations under the condition of pH7, 30 ℃ temperature, 50 mL liquid in 250 mL flask, 200 mg/L substrate and 1%(φ) inoculum size. In medium with lower concentration (50 mg/L) of oxytetracycline, 50 mg/L Zn²⁺ inhibited oxytetracycline degradation, while 50 mg/L Cu²⁺ inhibited oxytetracycline degradation in medium with higher concentration (200 mg/L) of oxytetracycline. DJ1 strain had high tolerance to tetracycline antibiotics and chloramphenicol, the tolerating concentrations to both were above 700 mg/L. DJ1 strain could grow on the plate of binary cross medium with antibiotics and heavy metals of Cu²⁺ and Zn²⁺, showing dual resistance to antibiotics and heavy metals.

Conclusion  DJ1 strain has high tolerance to tetracycline antibiotics, chloramphenicol, Cu²⁺ and Zn²⁺. It can efficiently degrade oxytetracycline and can be used to control antibiotic contamination in the environment.