Response mechanisms of marine microbial communities during sulfamethoxazole co-metabolic degradation

Antibiotics, as typical emerging contaminants posing significant ecological risks, are frequently detected in global coastal environments. Their biotransformation in marine environments depends on the stress responses of functional microbial communities, while the underlying response mechanisms remain unclear. Through integrated metagenomic and metabolomic approaches, this study systematically investigated the structural and functional responses of marine microbial communities during the co-metabolic degradation of sulfamethoxazole (SMX), a representative antibiotic. A marine microbial consortium was employed for SMX co-metabolism with alginate, prototypical marine natural organic matter, as the co-substrate. Results revealed that under SMX stress, the microbial community underwent a marked shift in OTU composition, alongside significant increases in richness and diversity. The dominant functional taxon Vibrionaceae exhibited a significant decrease in relative abundance from 97.0% to 82.7%, while Paracoccaceae with SMX degradation potential and other low-abundance (<0.01%) functional taxa were significantly enriched, collectively sustaining stable alginate metabolism and facilitating SMX co-metabolism. Co-occurrence network analysis revealed enhanced interspecies associations. Moreover, the functional profile of the microbial community was profoundly reshaped. Specifically, the microbial community activated adaptive responses, enhancing TCS activation, EPS and endospore production, flagellar motility and chemotaxis, antioxidant capacity and DNA repair, and antibiotic resistance, to mitigate the toxicity of SMX and its intermediates. Concurrently, metabolic strategies were altered via regulation of key pathways (e.g., carbohydrate metabolism and amino acid metabolism), which increased by 7.8% and 17.5% in relative abundance compared to the control, boosting energy supply and SMX-degrading enzyme synthesis to enable SMX co-metabolism. This study provides new insights into the response mechanisms of marine microbial communities to SMX stress and the ecological risk assessment of antibiotics in coastal waters.