Influence on denitrifying community performance by the long-term exposure to sulfamethoxazole and chlortetracycline in the continuous-flow EGSB reactors

The response of the denitrification community to long-term antibiotic exposure requires further investigation. Here, the significantly altered denitrifying community structure and function were observed by continuous exposure to 1 mg/L sulfamethoxazole (SMZ) or chlortetracycline (CTC) for 180 d in the expanded granular sludge bed reactors. Thaurea , positively correlated with SMZ and NO 3 − removal efficiency ( NrE ), was highly enriched in the SMZ-added reactor, while, Comamons and Acinetobacter were largely inhibited. The acute inhibited and then gradual-recovered NrE (87.17–90.38 %) was observed with highly expressed narG , indicating the adaptability of Thaurea to SMZ. However, the abundance of Thaurea and Comamonas greatly decreased, while Melioribacter and Acinetobacter were largely enriched in the CTC-added reactor. CTC created more serious and continuous inhibition of NO 3 − reduction ( NrE of 64.53–66.95 %), with lowly expressed narG . Improved NO 2 − reduction capacity was observed in both reactors (70.16–95.42 %) with highly expressed nirS and nosZ , revealing the adaptability of NO 2 − reduction populations to antibiotics.