Promote or inhibit? Transcriptomic and metabonomic insights into the effects of antibiotics on nitrogen uptake and metabolism in Myriophyllum aquaticum

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Phytoremediation is an effective nitrogen removal method to alleviate eutrophication. However, the coexistence of antibiotics may inhibit nitrogen removal by aquatic macrophytes, and the underlying mechanisms remain unclear. Here, we systematically investigated the effects of three antibiotics (norfloxacin, NOR; sulfamethoxazole, SMX; and oxytetracycline, OTC) at environmental concentrations (1 μg/L and 1 mg/L) on ammonia (NH4+–N) and nitrate (NO3-–N) removal by the aquatic macrophyte Myriophyllum aquaticum. NOR, SMX, and OTC reduced NH4+–N removal by M. aquaticum by 10–36 %, with low levels (1 μg/L) of NOR reducing NO3-–N removal by up to 60 %. Antibiotics substantially reduced the biomass and chlorophyll contents but increased the antioxidant enzymes in M. aquaticum. While antibiotics inhibited NH4+–N removal, the promotion or inhibition effect of antibiotics on NO3-–N removal by M. aquaticum depended on types and levels of antibiotics. Transcriptomic and metabonomic profile analyses revealed differentially expressed genes and metabolites, suggesting that the mechanisms underlying the promotional/inhibitory effects of antibiotics on nitrogen uptake and metabolism were related to ammonia metabolism, the tricarboxylic acid cycle, photosynthesis, and oxidative stress. Myriophyllum aquaticum exhibited better NH4+–N removal than NO3-–N removal, as NH4+–N can be directly taken up by M. aquaticum and transformed into ammonium, while NO3-–N must be absorbed by the plant and then reduced to ammonium. During this process, antibiotics disrupt genes associated with nitrogen uptake and metabolism. In this study, we provide multiomics insights into the mechanisms of nitrogen metabolism in aquatic macrophytes affected by antibiotics and offers a scientific basis for water pollution control.