Dose-response of floc sludge-based partial nitritation-anammox system to multiple antibiotics: Microbial community...

The mechanisms by which antibiotics affect floc sludge-based partial nitritation-anammox (PN/A) systems remain unclear. This study investigated the dose-response relationships and microbial adaptation mechanisms of the PN/A system under antibiotic exposure. Results demonstrated that the core nitrogen removal pathway of the PN/A system persisted, despite antibiotic-induced metabolic deceleration and biomass reduction. The floc sludge-based system exhibited resilience by recovering from low-dose antibiotic stress (10-100 μg/L) and even achieving enhanced nitrogen removal under high-dose exposure (200-1000 μg/L). This resilience was supported by three microbial strategies: (i) adaptive evolution dominated by Proteobacteria; (ii) enhanced interaction networks, as indicated by greater network complexity, calcium signaling pathway, two-component systems, and cell motility; and (iii) strengthened secretion systems for self-protection through elevated ABC transporters and biofilm formation. This study deciphers adaptive mechanisms of floc sludge-based PN/A systems to antibiotics and provides a scientific basis for their application in environments with fluctuating antibiotic stress.