Degradation of oxytetracycline in soil by a Pseudomonas strain

• OTC degradation by Pseudomonas strain T4 was the most effective under an initial OTC concentration of 2.5 mg kg -1 at 30°C in unsterilized soil. • Bacteroidetes, Proteobacteria and Acidobacteria played key roles in OTC degradation by T4 in the soil. • tet (G) was the most frequently detected among the 13 investigated tetracycline ARGs. Oxytetracycline (OTC) is used extensively in animal husbandry and enters the soil in different forms, causing severe environmental pollution. Previous studies have shown that the genus Pseudomonas can potentially degrade antibiotics in the soil environment. Environmental conditions, such as the initial concentration of antibiotics, incubation temperature and others, have significant impacts on the activity of antibiotic-degrading bacteria. However, few reports have clarified the environmental impacts on the effectiveness of Pseudomonas spp. In the present study, we investigated the effects of different initial concentrations of OTC and incubation temperatures, as well as soil sterilization, on OTC degradation by Pseudomonas <pg=>strain T4. We also focused on the microbial degradation pathways of OTC, and variations in both antibiotic resistance genes (ARGs) and microbial communities with T4 functioning under optimal conditions. The results showed that the most effective degradation occurred under an initial OTC concentration of 2.5 mg kg -1 at 30°C in unsterilized soil spiked with T4. These conditions yielded an OTC degradation rate of 69.53% within 63 days. The putative degradation pathways of OTC in the presence of T4 included dehydration, demethylation, deamination, hydroxylation, oxidation and ring opening. Bacteroidetes, Proteobacteria and Acidobacteria played key roles in the biodegradation of OTC with T4 in the soil. The results also showed that tet (G) was the most frequently detected among the 13 common tetracycline ARGs that were investigated. The bacterial community shift observed in this study may provide new insights into the microbial degradation of OTC in soil.