Insight into the microbial and genetic response of anammox biomass to broad range concentrations of different antibiotics: Linking performance and mechanism

Antibiotics have become emerging pollutants occurring in wastewater, influencing the activity of microorganisms responsible for wastewater treatment. Moreover, the potential application of the anammox process in the treatment of antibiotic-containing wastewater has paid much attention. A common antibiotic, OTC (oxytetracycline), CIP (ciprofloxacin), and CLA (clarithromycin) are recognized to be monitored in wastewater due to their relatively high concentration and hazardous impact on the environment. However, their effect on the anammox process remains unknown. Therefore, this paper presents the study concerning the long-term effects of a successive concentration of three antibiotics (OTC, CIP, CLA) on the anammox process, with special emphasis on treatment efficiency, resistance mechanism, bacteria cell morphology, and activated sludge community structure. It is worth noting that the influence of a successive concentration of CIP and CLA has been studied for the first time. Results revealed that anammox community could adapt to CIP, OTC, and CLA at low concentrations (<1 mg L-1), while the high concentration of antibiotics (100 mg L-1) reduced the nitrogen removal rate (NRR) by 27 % (OTC), 30 % (CIP), and 56 % (CLA). Community structure analysis showed that the abundance of Planctomycetes increased with the increase of CIP and CLA concentration while decreasing under OTC stress. On contrary, other nitrogen-cycle bacteria (e.g., Nitrospira) contributed to the nitrogen removal, especially during antibiotic suppression. The abundance of corresponding ARGs (OTC resistance gens: tetX, tetC, tetW, CIP resistance gens: qnrB4, qnrS, CLA resistance gens: mphA) generally increased under antibiotic suppression. In addition, co-occurrence analysis showed that anammox bacteria might participate in the transfer of macrolide resistance genes. The findings of this study are essential in understanding the mechanisms of three antibiotics commonly occurring in wastewater during the anammox process. Moreover, the results have implications for using the anammox process for antibiotic-containing wastewater treatment and provide the operational guidance for stable conducting of the anammox process under antibiotics suppression.