Dynamics of antibiotic resistance genes and microbial community in shortcut nitrification-denitrification process under antibiotic stresses.

In this study, the performance of shortcut nitrification-denitrification (SCND) at different TC and SD stress conditions (0 μg/L, 1-97 days; 100 μg/L, 98-138 days; 500 μg/L, 139-175 days) was investigated. Higher level antibiotic stress (500 μg/L) led to the serious deterioration of nitrogen removal, and denitrification was more sensitive to antibiotic stress than nitrification. The dynamics of antibiotic resistance genes (ARGs) and microbial community were revealed by quantitative real-time PCR and 16S rDNA high-throughput sequencing, respectively. Tet-genes (tetA, tetQ, tetW), sul-genes (sulI, sulII), and mobile genetic element (intI1) in activated sludge increased by 1.2 ~ 2.5 logs with long-term exposure of antibiotic stress, and sulI, tetA, tetQ, and tetW were significantly positively correlated with intI1. Long-term antibiotics stress caused the decrease of most denitrifiers, and five genera were identified as the potential host of ARGs. The key impact factors of SCND drove the dynamics of ARGs and microbial community. Except for sulII gene, DO and FA were significantly positively correlated with ARGs, while FNA, NAR, and NO-N showed opposite effects to ARGs. Overall, maintaining relative lower DO, higher FNA, NAR, and NO-N conditions are not only benefit to the stable operation of SCND, but may also conducive to the control of ARG dissemination. This study provides theoretical basis on the control of ARGs in the SCND process.