Metal-Ion-Assisted Biodegradation of Sulfamethoxazole by Multidrug-Resistant Atlantibacter hermannii Isolated from Hospital Wastewater

The widespread release of sulfonamide antibiotics into aquatic environments has become a major environmental and public health concern due to their persistence and contribution to antimicrobial resistance dissemination. In the present study, a multidrug-resistant (MDR) bacterial isolate capable of degrading sulfamethoxazole (SMX) was recovered from hospital wastewater collected in Bangladesh and identified as Atlantibacter hermannii by 16S rRNA gene sequencing. Antibiotic susceptibility testing revealed resistance to 13 out of 14 tested antibiotics, including sulfamethoxazole, confirming its MDR phenotype. The biodegradation potential of the isolate was evaluated in mineral salts medium supplemented with SMX under different physicochemical and metal-ion conditions. Among the tested transition metals, iron supplementation produced the greatest enhancement of bacterial growth and presumed SMX degradation, followed by manganese, whereas copper markedly inhibited bacterial activity. Optimization experiments demonstrated that 5 mM FeSO₄ was the optimal iron concentration for degradation. Combined Fe and Mn supplementation further improved degradation efficiency, with the Fe:Mn molar ratio of 1:2 yielding the highest growth response. pH optimization revealed that alkaline conditions (pH 8) were most favorable for Mn-mediated degradation. Ethanol co-supplementation enhanced Fe-mediated degradation up to 0.5% (v/v), but completely inhibited Mn-mediated degradation, suggesting mechanistic differences between iron- and manganese-associated pathways. Collectively, these findings provide the first evidence of SMX biodegradation by Atlantibacter hermannii and demonstrate the importance of transition metal optimization in enhancing antibiotic bioremediation. The study highlights the potential application of metal-assisted bacterial systems for the treatment of sulfonamide-contaminated hospital wastewater in resource-limited settings.