Profiles and potential mobility of antibiotic resistance genes in different bioelectrochemistry-enhanced constructed wetlands

Antibiotic resistance genes (ARGs) in aquatic environments have been highlighted on a global scale because of their risks to public health. Bioelectrochemistry-enhanced constructed wetlands have great potential for reducing the abundance of ARGs. However, the profiles of ARGs and their mobility in different bioelectrochemistry [microbial fuel cell (MFC) and micro direct current (EC)]-enhanced constructed wetlands (CW) are unclear. In this study, the occurrence of sulfonamide resistance genes (sul ARGs) in effluent and substrate and their potential mobility and hosts in MFC-CWs and EC-CW were determined by quantitative PCR and metagenomics approach under the continuous input of sulfamethoxazole (SMX). The results showed that the relative abundance (RA) of sul ARGs in the effluent and the lower substrate layer were decreased by bioelectrochemical technology owing to high SMX removal and the expansion of bacteria without ARGs. However, the RA of sul ARGs in the EC-CW was higher than that in the MFC-CW. Based on metagenomic analysis, SMX promoted the co-selection of the non-corresponding types of ARGs and corresponding types of sul ARGs in the EC-CW and MFC-CW, and ARGs mediated by plasmids were more prevalent than those encoded in chromosomes. Bacitracin ARGs and sul ARGs were the dominant types, and the dominant subtypes of ARGs in the EC-CW and MFC-CW were similar, with only sul1 showing significant difference (p < 0.01). An obvious difference in the proliferation and mobility of ARGs between the EC-CW and MFC-CW was observed. The abundance of dominant hosts for sul ARGs and the distribution of ARGs and mobile genetic elements might result in differences in sul ARGs in the EC-CW and MFC-CW.