Antibiotic stress drives nutrient transformation in constructed wetlands via microbial community and metabolic shifts

The pervasive use of antibiotics (ATB) in aquaculture results in their persistent discharge into water bodies, constituting a continuous source of environmental contamination; constructed wetlands (CWs) are commonly employed to treat aquaculture wastewater in southern China, yet the mechanisms by which ATB affect conventional pollutant removal remain poorly understood. In this study, a quartz sand-based vertical-flow CW system was established with a control and an ATB-treated group (spiked with 500 μg·L −1 each of tetracycline, oxytetracycline, and ofloxacin), and continuous operation experiments were conducted to evaluate the effects of ATB on chemical oxygen demand, nitrogen, and phosphorus removal, while metagenomic sequencing was used to analyze microbial community structure and functional potential. Results showed that ATB significantly inhibited removal efficiencies for all test pollutants, with phosphorus exhibiting the greatest decline (from 85.0% to 72.5%), and the average removal rates of the three-target ATB ranged from 67.6% to 70.3%. Microbial community restructuring was evident, with Proteobacteria decreasing and Cyanobacteria increasing in relative abundance; although the abundances of typical polyphosphate-accumulating organisms remained unchanged, the relative abundances of ppk and genes encoding key enzymes in glycolysis and the tricarboxylic acid cycle were significantly lower, suggesting that ATB reduced the functional potential for central carbon metabolism, thereby potentially curtailing the energy supply for phosphorus uptake. Regarding nitrogen metabolism, the key gene nrfA , which encodes dissimilatory nitrate reduction to ammonium (DNRA), had a markedly higher relative abundance, favoring DNRA over denitrification and thus contributing to reduced total nitrogen removal. Overall, this study highlights that functional potential is more indicative than abundance changes, providing a basis for optimizing CW performance under ATB pollution.