Abstract:
A strain CQ2, which can degrade antibiotic cephalexin effectively, was separated from the sludge of domestic sewage treatment plant, and was identified as
Ochrobactrum sp. The strain was identified as gram-negative bacteria with a diameter of 4—6 mm. Under 1000 times optical microscope, CQ2 was rod-shaped with a diameter of 0.4—0.6 μm and a length of 1.2—2.5 μm. This strain could not efficiently degrade CX when CX was the only organic carbon source, but could decompose CX rapidly in the presence of glucose, indicating that the strain removed CX through a co-degradation mechanism. The effects of temperature, pH, rotating speed and inoculation percentage on the growth and degradation efficiency of CQ2 were investigated by orthogonal tests. The results showed that CQ2 could effectively degrade cephalexin, and the optimal cultivation conditions are temperature of 30 ℃, pH at 7.0, mixing rate of 150 r/min, and inoculation percentage of 5%. Under the optimal conditions, the cephalexin at initial mass concentration of 10 mg/L could be completely degraded within 28 h. Moreover, under the identical conditions, the tested CQ2 could completely remove amoxicillin at 36 h and significantly degrade terramycin and sulfadiazine, while it played a negligible role on the degradation of pefloxacin due to the inhibition on the CQ2 growth. It is possible that the chromosome of pale bacillus contains specific AmpC gene, which can produce the cephalosporin enzyme ApmC, and therefore has strong resistance to amoxicillin and cefalexin with the structure of
β-lactam ring. Based on cephalexin degradation intermediates determined by LC-MS/MS, the biodegradation preliminary pathway of cephalexin by CQ2 was proposed, and 2-hydroxyl-3-phenylpyrazine was the main intermediate of biodegradation after hydrolysis.