Abstract: This study aims to elucidate nicosulfuron degradation pathway of Pseudomonas geniculate strain XZ4 and identify its key functional genes. The findings will provide a theoretical basis and genetic resources for deciphering the strain's degradation mechanism, expanding gene repositories, and developing efficient nicosulfuron-degrading microbial agents and enzymatic preparations. Using the previously screened nicosulfurondegrading strain XZ4 as the research subject, the degradation conditions were optimized through single-factor experiments and response surface methodology (RSM). The degradation pathway was inferred via liquid chromatography-mass spectrometry (LC-MS), and potential degradation-related genes were predicted through whole-genome analysis. The optimal degradation conditions for strain XZ4 were determined as temperature of 28.51°C, value of pH 7.22 and inoculum size of 3.83%. Under these conditions, the strain achieved a degradation rate of 96.28% for 100 mg/L nicosulfuron within 5 days and demonstrated tolerance and degradation capability for concentrations up to 250 mg/L. Four intermediate metabolites were detected by LC-MS. Based on the chemical structure of nicosulfuron and metabolomic analysis, the degradation pathway involves two critical routes, cleavage of the sulfonylurea bridge C-N bond and sulfonylurea bridge C-S bond. Whole-genome functional annotation and comparative genomic analysis identified eight candidate genes encoding esterases and hydrolases potentially involved in nicosulfuron degradation. Strain XZ4 exhibits robust nicosulfuron tolerance and degradation capacity, offering novel microbial and enzymatic tools for environmental pollution remediation.

Key words: nicosulfuron, Pseudomonas geniculate XZ4, degradation characteristics, action mechanism