The effect of extracellular polymeric substances on the distribution and transmission of antibiotic resistance genes treating antibiotic wastewater via microbial electrolysis cells

Microbial electrolysis cells (MEC) have emerged as a prominent technology for the treatment of antibiotics-containing wastewater in recent years. However, there remains a dearth of comprehensive exploration regarding the influence of extracellular polymers substances (EPS) on the distribution and transmission of antibiotic resistance genes (ARGs) in MEC. In this study, we quantified the distribution of ARGs in MEC by Fluorescence quantitative polymerase chain reaction and explored with emphasis on impact of EPS component on ARGs transmission at under different concentrations of roxithromycin. Results showed that the absolute abundance of ARGs in the electrode biofilm was 1 - 2 orders of magnitude higher than that in the anolyte. Specifically, EPS-associated ARGs accounted for 2.31% - 11.18% of ARGs in electrode biofilm. The presence of elevated roxithromycin concentration led to electroactive microorganisms (Geobacter and Geothrix) as potential hosts of ARGs. In addition, both protein and polysaccharide content in the electrode biofilm increased with increasing roxithromycin concentration and showed positive correlations with EPS-associated ARGs. Fluorescence quenching experiments further elucidated that tryptophan and tyrosine residues in EPS could bind to ARGs effectively, contributing the hindering the ARGs transmission between hosts. Therefore, increased EPS content within electrode biofilm could reduce the concentration of ARGs present in anolyte while also influencing ARGs distribution throughout MEC. This study provides valuable insights into the distribution of ARGs in MEC systems and the role of EPS in regulating ARGs migration.