Abstract: In order to explore the microbial strain resources for chloramphenicol degradation, a chloramphenicol-degrading strain CC18 was isolated and screened from the activated sludge in the biological contact oxidation reactor treating chloramphenicol wastewater. The CC18 was identified as Pseudoxanthomonas mexicana based on its morphological, physiological and biochemical characteristics, and 16S rRNA gene sequence analysis. The optimal conditions for degradation chloramphenicol by strain CC18 were 4% inoculum, pH 7, and at incubation temperature 28 ℃. The degradation efficiency of 20 mg/L chloramphenicol after 24 h was 22.9%. The response surface results further suggested that the degradation efficiency of 20 mg/L chloramphenicol by strain CC18 was 30.6% after 24 h when the inoculum was 3.6%, pH was 7.6, and the temperature was 30 ℃. The ability of Pseudoxanthomonas mexicana to degrade chloramphenicol was found for the first time in this study, which not only enriched the chloramphenicol degrading bacterial resource, but also provided a theoretical basis for the microbial enhancement treatment of chloramphenicol contamination in the environment.

Key words: chloramphenicol, Pseudoxanthomonas mexicana, isolation, identification, microbial degradation