Enhanced biodegradation of sulfamethazine in swine manure composting: Pathway elucidation, mechanism insights, and optimization of a novel Bacillus sp. strain

Sulfamethazine (SMZ), a widely used sulfonamide antibiotic frequently detected in livestock waste streams, requires enhanced microbial degradation strategies to prevent its accumulation and associated environmental hazards. While several microbial strains with SMZ degradation capability have been isolated, comprehensive elucidation of metabolic pathways remains incomplete. This study identified Bacillus sp. strain DLY-11, exhibiting exceptional SMZ degradation performance, from thermally treated swine manure compost substrates. Under optimized parameters (5 % (v/v) bacterial inoculum, 59.7 °C operational temperature, pH 8.08 maintained with buffer system, and 0.4 g/L MgSO 4 supplementation), the strain achieved 97.1 % elimination of 20 mg/L SMZ within 48-h incubation. Metabolic pathway analysis through detected intermediates revealed two distinct biodegradation mechanisms involving sulfonamide bond cleavage, oxidative hydroxylation, sulfur dioxide elimination, ring oxidation, amino group substitution, and glucuronic acid conjugation. These findings enhance understanding of sulfonamide antibiotic catabolism while offering a promising microbial resource for controlling veterinary antibiotic contamination in agro-industrial ecosystems. • Isolation of highly efficient SMZ-degrading bacterial strains from pig manure compost. • Under optimal conditions, the DLY-11 strain degraded 97.1 % of SMZ within 48 h. • Two potential SMZ degradation pathways were proposed. • S-N bond cleavage, hydroxylation, and SO 2 release are common degradation mechanisms.