Deciphering the degradation pathway and acclimation-driven adaptive evolution characteristics of a novel sulfamethoxazole-degrading strain Bacillus cereus SDB-X

A novel SMX-degrading strain, Bacillus cereus SDB-X , was isolated and achieved high SMX degradation. • Strain SDB-X degrades SMX through acetylation, desulfonylation, and hydroxylamination pathways. • Adaptive mutation in the key gene menC increased enzyme–substrate binding affinity, lowering the binding energy from −8.3 to −8.6 kcal/mol. • Long-term acclimation upregulated the expression of key degradation genes, facilitating the adaptive evolution of SDB-X's SMX-degrading capability. • In complex aqueous matrices, the SDB-X strain demonstrated consistent SMX removal efficiency. Sulfamethoxazole (SMX), a widely distributed emerging contaminant, poses risks to ecosystems and public health. Microbial degradation offers an efficient and eco-friendly remediation strategy. In this study, a SMX-degrading strain was isolated from hospital wastewater and identified as Bacillus cereus SDB-X. The original strain (SDB-X00) degraded 89% of 50 mg/L SMX within five days, and after 60 days of acclimation under SMX stress, the degradation efficiency increased to 96%. Kinetic analysis revealed that the acclimated strain SDB-X60 exhibited the fastest degradation rate ( k  = 0.721 d −1 , t ₁/₂ = 0.96 d). Moreover, SDB-X60 maintained stable degradation activity in a complex wastewater matrix. LC-MS/MS analysis proposed a tentative SMX metabolic pathway involving N -acetylation and typical intermediate metabolites. Genomic analysis identified several candidate degradation-related genes; a mutation in SDB-X60 altered the MenC protein substrate binding free energy from −8.3 to −8.6 kcal/mol. Transcriptomic analysis further indicated upregulation of degradation-related genes after acclimation. This study expands understanding of SMX biodegradation by B. cereus and highlights the role of acclimation in enhancing degradation activity, providing a theoretical basis for bioremediation of antibiotic-contaminated environments.