Chronic exposure to environmentally-relevant sulfamethoxazole alters ammonia-oxidizing microbial communities in...

Managed aquifer recharge (MAR) is a critical technology for water resource management and purification, yet its capacity to remove antibiotics remains limited. Understanding the response of ammonia-oxidizing microorganisms (AOMs) to antibiotics exposure is essential for optimizing MAR-based antibiotic mitigation strategies. This study investigated the long-term effects of sulfamethoxazole (SMX, ∼500 ng/L) on AOM communities through a 20-month controlled MAR column experiment. Results showed that AOMs (0.4-3.7 % of total microbial abundance) were dominated by ammonia-oxidizing archaea (AOA, 10.2-82.9 %) and complete ammonia oxidizers (comammox, 15.4-89.7 %), with negligible ammonia-oxidizing bacteria (AOB, <2.4 %). Chronic effects of SMX resulted in a 60-67 % reduction in amoA genes across AOA, AOB, and comammox populations, indicating a significant threat to nitrogen cycling. Specifically, SMX suppressed 2-7 AOA metagenome-assembled genomes (MAGs) (e.g., Nitrosotenuis) by 57-95 % and 4-5 comammox MAGs (e.g., Nitrospira) by 23-82 %. Conversely, SMX increased 4-7 AOA MAGs (e.g., Nitrosarchaeum) by 1.4-24.3-fold and 2 comammox MAGs (e.g., Nitrospira) by 1.9-2.0-fold, revealing taxon-specific tolerance. Notably, AOA lineages demonstrated superior resilience to SMX compared to comammox. These findings advance our understanding of antibiotic-driven microbial community dynamics in MAR systems and provide valuable insights for enhancing their performance in antibiotic-polluted environments.