Isolation of an oxytetracycline-degrading bacterial strain and its biodegradation characteristics

Objectives With the rapid development of intensive livestock breeding, the use of antibiotics has been increased sharply, which results in a large amount of antibiotics residuals and drug-resistant bacteria in solid waste and sewage. The improper discharge of these solid waste and sewage leads to accumulation of antibiotics and drug-resistant bacteria in soil and water. As one of the main antibiotics used in animal husbandry industry, high residual content of oxytetracycline exists in animal manure and sewage. Effective strains need to be developed for the efficient degradation and cleanup of residual oxytetracycline.

Methods A method of enrichment and acclimation was applied to screen oxytetracycline degradation bacteria from microbial fertilizers, antibiotic fermentation residues and livestock manures. The screened strains were identified using the 16S rDNA sequencing technology. Oxytetracycline content was determined using high performance liquid chromatography (HPLC) method. The biodegradation condition of oxytetracycline by the screened bacteria was optimized under different temperature, pH, rotation speed and inoculum size.

Results The screened strain of T4 was found capable of efficiently degrading oxytetracycline, and was identified as Pseudomonas sp. The degradation rate of oxytetracycline was the highest (26.75%) at 30℃, and was 27.03% at pH 7. When the rotation speed was 150 rpm and 170 rpm, oxytetracycline showed higher degradation rates of 26.18% and 25.59%, respectively. Considering the high energy consumption of the high-speed shaking, 150 rpm was chosen as the optimal speed. The inoculation was negatively correlated with the degradation of oxytetracycline, and finally 1% of inoculum size was chosen as the optimized one. The highest oxytetracycline degradation rate was 26.29% under the final optimized condition at the medium of 100 mg/L oxytetracycline. In addition, the composting experiment showed that T4 could effectively improve the degradation of oxytetracycline during composting.

Conclusions The strain of T4, identified as Pseudomonas sp., is proved to be capable of degrading oxytetracycline efficiently. The optimized conditions are 30℃, pH 7.0, 150 rpm, and 1% of inoculum size. The composting test showed that the T4 had a positive effect on the degradation of oxytetracycline, indicating potential of using the T4 as oxytetracycline degrading bacterium in environment pollution prevention.