Response of performance, antibiotic resistance genes and bacterial community exposure to compound antibiotics stress: Full nitrification to shortcut nitrification and denitrification

The long-term effects of compound antibiotics stress (50-200 mu g/L tetracycline (TC), sulfadiazine (SD) and ciprofloxacin (CIP)) on the transmission of nitrogen removal process from full nitrification to shortcut nitrification and denitrification (SCND) were evaluated in this study, with the focus on pollutants removal performance, antibiotic resistance genes (ARGs) and bacterial community. Results showed that compound antibiotics could promote the process from full nitrification to SCND due to the enrichment of functional bacterial community, in which the removal rates of total nitrogen increased by 51.24%-60.36%. In the whole process, the correspondence between antibiotic types and ARG subtypes was not one-to-one. Compared with full nitrification, the increase rates of ARGs/MGEs and the total environmental risks in SCND were gradually decreased, indicating SCND had a stronger stability even stress on 4 times antibiotics. The main functional denitrifying genera (Brachymonas) in SCND were far higher than that in full nitrification, but it was not identified as potential hosts of TC, SD and CIP. The Network analysis and Partial least-squares path model (PLS-PM) further confirmed that ARGs/ MGEs could be controlled by regulating environmental factors. This study provides an insight into the effects of compound antibiotics on SCND, and guides future efforts to control antibiotic and ARGs pollution in wastewater treatment.