Zero valent iron modified carriers can promote anammox resistance to tetracycline hydrochloride stress

Abstract

The toxic effects of antibiotics on anammox bacteria (AnAOB) draw much attention. Zero valent iron (ZVI) can improve anammox performance, but whether ZVI promotes resistance to antibiotics stress is unknown. In this study, the effect of tetracycline hydrochloride (TCH) on anammox in the 10 wt% ZVI modified carrier filled system (R1) was investigated. Results showed that semi-inhibitory concentration (IC50) of TCH in R1 was 30.93 mg/L. In comparison, IC50 of TCH in R0 filled with conventional carriers was only 18.87 mg/L. Long-term effects showed that the inhibition of anammox biofilm by low concentration of TCH (≤ 50 μg/L) was not significant, whereas R1 exhibited better anammox performance than R0 when TCH was 100–200 μg/L. More extracellular polymeric substances (EPS) on the modified carriers was beneficial to trap TCH to mitigate toxicity. In addition, the heme-c contents and the enzymatic activities of NIR, HZS, HDH of R1 were higher than those of R0 regardless of the TCH dosing. The synergistic TCH degradation bacterium Ignavibacterium was enriched in R1, which might further mitigate the toxic effect of TCH. qPCR results of antibiotic resistance genes (ARGs) showed tetX, tetA and tetG were up-regulated on ZVI modified carrier, implying more enzymes were produced to inactivate and pump out TCH to resist the stress.