Response surface methodology and Box-Behnken design optimization of Sulfaquinoxaline removal efficiency and degradation mechanisms by Bacillus sp. strain DLY-11

Antibiotic pollution, particularly the persistence of Sulfaquinoxaline (SQ) residues in livestock and poultry farming environments, has emerged as a pressing environmental concern. Despite this, there remains a limited understanding of the optimized conditions and mechanisms for the efficient degradation of SQ by microorganisms. To address this knowledge gap, we isolated Bacillus sp. strain DLY-11 from aerobically composted manure, which exhibits exceptional SQ degradation capability. Using response surface methodology and Box-Behnken design, we optimized the conditions: 5 % inoculum, 60 °C, pH 8.02, and 0.5 g/L MgSO₄. Strain DLY-11 achieved 95.5 % SQ degradation in 2 d. We identified 12 degradation products, including one newly reported, and proposed four degradation pathways involving S-N and C-N bond cleavage, hydroxylation, SO₂ release, deamination, oxidation, acetylation, and formylation. One of the proposed pathways is entirely new and has not been previously reported in the literature. This work closes important information gaps in the bacterial degradation pathways of SQ by optimizing the degradation conditions and introducing a useful microbial resource for the effective breakdown of SQ. It also provides a solid theoretical foundation for tackling the problem of antibiotic contamination in livestock and poultry production.