Comprehensive analysis of biotransformation pathways and products of chloramphenicol by Raoultella Ornithinolytica CT3: Pathway elucidation and toxicity assessment.

Microbial degradation of chloramphenicol (CAP) has become important for reducing the adverse impact of environmental pollution with antibiotics. Although several pathways for CAP degradation have been identified in various bacteria, multiple metabolic pathways and their respective intermediate metabolites within a single strain are rarely reported. Here, Raoultella ornithinolytica CT3 was first isolated from silkworm excrement using CAP as the sole carbon source, and 100 mg/L CAP was almost completely degraded within 48 h. The biodegradation type of CAP followed first-order kinetics. Twenty-two CAP biotransformation products were identified using high-performance liquid chromatography and ultra-high-performance liquid chromatography coupled with high-resolution mass spectrometry. The CAP biotransformation pathways were predicted mainly in the acetylation and auxiliary pathways of propionylation and butyrylation. The toxicity of CAP biotransformation products was evaluated using the ecological structure-activity relationship (ECOSAR) model and biological indicators. The results showed that the toxicity of the intermediate metabolites changed slightly, but the final metabolite was harmless to the environment. Genomic analysis predicted that genes encoding acetyltransferase, amido-linkage hydrolase, nitroreductase, haloacetate dehalogenase, and protocatechuate 3,4-dioxygenase were associated with CAP biodegradation. This study provides new insights into the microbial degradation pathway of CAP and constitutes an ecological safety assessment for CAP-contaminated environments.