Efficient Biodegradation of Cefixime by the Newly Isolated Strain <i>Pseudochrobactrum asaccharolyticum</i> TY12 and Insights into Its Degradation Mechanism

Cephalosporin residues in agricultural soils, food systems, and aquatic environments pose severe threats to food safety, public health, and the ecological environment. While biodegradation represents a promising remediation strategy, the degradation mechanisms for most cephalosporins remain elusive. In this study, Pseudochrobactrum asaccharolyticum TY12 was isolated and demonstrated a broad-spectrum ability to degrade multiple cephalosporins. Notably, strain TY12 exhibited the highest cefixime (CFX) degradation efficiency, achieving a 93.87% removal of 100 mg/L CFX within 12 h. Ten degradation products of CFX were identified via high-resolution mass spectrometry, leading to a proposed degradation pathway. Notably, these products exhibited significantly attenuated antibacterial activity. Transcriptomic analysis and heterologous expression identified β-lactamase TY3865 as the key enzyme. Furthermore, molecular docking and site-directed mutagenesis revealed the residues critical for its catalytic activity. These findings provide mechanistic insights into antibiotic biodegradation and demonstrate the potential of TY12 for treating cephalosporin-contaminated wastewater.