Abstract:

Nitrate and antibiotic pollutions in water have attracted much attention in recent years, but the effects of combination antibiotic pollution on the biological water denitrification process is not clear. To address this issue, we tested norfloxacin and lomefloxacin under simulated experimental conditions. The $\text{NO}_{3}^{-}$-N and $\text{NO}_{2}^{-}$-N degradation results showed that lomefloxacin and norfloxacin had different inhibitory effects on water denitrification: Lomefloxacin promoted denitrification slightly in the early stage but inhibited it later on, whereas norfloxacin only inhibited it. Lomefloxacin combined with norfloxacin were less inhibitory than norfloxacin alone, and the combination showed antagonistic activity. The inhibitory activities of antibiotics ranked as norfloxacin > norfloxacin + lomefloxacin > lomefloxacin. Although the simulated experimental conditions did not fully match the actual water condition, the above results implied that combination antibiotics have antagonistic effects on the denitrification process. Such effects were related largely to the microbial numbers and activities, activities of denitrification enzymes, as well as abundance variations of dominant denitrifying bacteria Achromobacter xylosoxidans, Acinetobacter baumannii, and Pseudomonas sp. KY and the nosZ and aac genes. As reaction time increased, the denitrifying bacteria gradually adapted to the environment of low-level antibiotics and the number of quinolone resistance genes increased; also on the rise were the amount and activities of denitrifying bacteria, activities of denitrification enzymes, and microbial communities.

Key words: nitrate, antibiotic compound, denitrification, antagonism