A novel metronidazole-degrading bacterium Sphingopyxis sp. K5: isolation, characterization, and application potential in soil and wastewater remediation

Metronidazole is a widely used nitroimidazole antibiotic in clinical practice. Following its widespread use, it enters the environment via medical wastewater, posing a potential risk of toxicity to ecosystems and living organisms. Microbial degradation is an efficient method of accurately eliminating target pollutants from the environment. Here, a metronidazole degrader, Sphingopyxis sp. K5, was isolated from medical wastewater sludge. Strain K5 could degrade 58.7 μM metronidazole after 4 days of incubation with an initial OD600 of 1.5. The optimal degradation conditions were 35°C and pH 8.0, and the strain exhibited stable degradation efficiency on high metronidazole concentrations (100-500 μM). The supplementation of nutrients such as LB or glucose can improve degradation efficiency by 152.0% and 129.0%, respectively. Design-Expert software was used for optimization of conditions such as temperature (33.7°C), pH (8.2), and cell density of inoculation (OD600 of 1.0). The degradation of metronidazole in soil and wastewater by strain K5 proved its potential for application. Strain K5 could eliminate > 95% of 5 and 25 ppm metronidazole in soil and wastewater within 5 and 10 days, respectively. Our results characterized the degradation efficiency of metronidazole by strain K5 and provided a theoretical basis for the bioremediation of metronidazole-contaminated environments.