Constructed wetlands are a low-cost, low-energy and environmentally friendly wastewater treatment technology. Constructed wetlands have potential of removal of antibiotics and antibiotic resistance genes. However, there is a little understand on public health risks of antibiotic resistance genes in effluent from constructed wetlands treating wastewater in the presence or absence of antibiotic residues. In order to investigate public health risks for effluent-receiving environment, we prepared two different experimental constructed wetlands treating tetracycline-contaminated (230 μg/L) and tetracycline-uncontaminated wastewater and examined changes in the abundances of the tetracycline resistance genes tetA, tetC and tetX and the microbial community composition in effluents from both constructed wetlands. We monitored tet genes by realtime PCR and analyzed microbial community composition by 16S rRNA gene amplicon sequencing. The constructed wetlands showed a strong ability to remove tet genes from wastewater, which reduced their risk to the public in the effluent-receiving environment. However, the presence of tetracycline antibiotic in wastewater, even at a sub-inhibitory concentration, could lessen the removal ability of constructed wetlands and change the microbial community composition. The propagation of Chlamydiae and Gammaproteobacteria also increase in the presence of tetracycline. Given that Chlamydiae and Gammaproteobacteria include many human and animal pathogens, this result highlights their persistence and development under tetracycline contamination and the potential adverse effects on human and environmental health. This appears to be the first report of the selective pressure and promoting effects of tetracycline on tet gene abundance and microbial community composition in common reed constructed wetlands.
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