Acute and chronic responses of nitrifying culture under moxifloxacin exposure

Batch tests and continuous operation were conducted to evaluate the acute and chronic responses of nitrifying culture under moxifloxacin exposure. The results showed that nitrifying culture exhibited limited capacity for adsorption and biodegradation of moxifloxacin. Ammonium and nitrite oxidation were inhibited by 10 mg/L moxifloxacin within 4 h, reducing nitrite oxidation efficiency by 10%. However, the ammonium oxidation rate gradually recovered to pre-exposure level and developed tolerance during long-term exposure, while the nitrite oxidation rate failed to recover even after the recovery period. Further studies revealed that the inhibition of nitrification was driven by increased reactive oxygen species and decreased activities of ammonium monooxygenase and nitrite oxidoreductase. The absolute and relative abundances of the predominant genus Nitrosomonas continuously increased during exposure, suggesting that moxifloxacin had no adverse effect on the growth of ammonium-oxidising bacteria.