Methanogenic efficiency of anaerobic digestion under sulfaquinoxaline sodium (SQ-Na) stress: Insights from enzyme, microbial community and metagenome analyses

Sulfaquinoxaline sodium (SQ-Na), a veterinary sulfonamide antibiotic, poses potential risks to anaerobic digestion (AD) systems due to its antimicrobial properties, yet its impacts on methanogenic efficiency and microbial dynamics remain poorly understood. This study systematically evaluated the effects of SQ-Na (0–50 mg/L) on AD of simulated wastewater through batch experiments, integrating methane yield analysis, enzyme activity assays, 16S rRNA sequencing and metagenomic insights. Results demonstrated a dose-dependent inhibition of cumulative methane production, with 1 and 5 mg/L SQ-Na reducing yields to 41.21 % and 8.12 % of the control, respectively, while 20–50 mg/L caused near-complete stagnation. The modified Gompertz equation revealed prolonged lag phases (up to 53.52 % extension) and suppressed maximum methane production rates (Rmax). Function enzyme analyses indicated SQ-Na-induced adenosine triphosphatase (ATPase) inhibition (0.26–0.63–fold reduction) alongside accumulated Acetyl-CoA (A-CoA, 0.23–2.32 folds) and Coenzyme F 420 (F 420 , 0.48–2.52 folds), suggesting metabolic imbalance. Microbial shifts highlighted SQ-Na-driven suppression of acetoclastic methanogens (e.g., Methanosaeta ). Metagenomic evidence further pinpointed decreases in the abundance of methanogenesis-associated genes (e.g., EC 7.2.1.4, EC 2.8.4.1) and folate biosynthesis pathways, revealing an inhibition mechanism where SQ-Na competitively inhibits dihydropteroate synthase (EC 2.5.1.15), impairing the metabolic chain of energy, enzymes and function substances. This study offering critical data for optimizing SQ-Na-wastewater treatment and sustainable bioenergy recovery.