Biochar-based composite drives sulfadiazine sequestration and mitigates active resistome risks

Soils are major reservoirs of antimicrobial resistance genes. Understanding how remediation strategies influence the specific bacteria responsible for antibiotic degradation remains both critical and challenging. Here, we use DNA stable-isotope probing to identify the active sulfadiazine-degrading microbiome and show that a biochar-biofilm composite carrying Arthrobacter D2 modulates resistance dynamics. In a less fertile Ultisol, the composite accelerated the removal of extractable sulfadiazine from bulk soil and reduced the total abundance of antimicrobial resistance genes and virulence factors. The more fertile Mollisol showed overall community resilience; however, targeted analysis of active sulfadiazine degraders revealed reduced diversity of resistance determinants in both soils. Importantly, distinguishing active sulfadiazine degraders from the total community uncovered resistance dynamics that bulk soil analyses failed to detect. These findings demonstrate that biochar-biofilm strategies can suppress resistance potential among key antibiotic-degrading bacteria, thereby potentially enhancing ecosystem safety in low-fertility soils.