Biochar reduces plasmid-mediated antibiotic resistance gene transfer in earthworm ecological filters for rural sewage treatment

Abstract

The spread of antibiotic resistance genes (ARGs) in rural wastewater threatens both ecological environment and human health. Earthworm ecological filters (EEFs) represent a green technology for rural sewage treatment. However, their effectiveness in removing ARGs remains a significant challenge. This study aims to investigate the role and underlying mechanisms of biochar addition in enhancing ARGs removal in rural sewage using EEFs. To achieve this, the fate of chromosome- and plasmid-carried ARGs was quantified in constructed EEFs, both with and without biochar addition. The results showed that the biochar could effectively remove ARGs from rural sewage, with a better removal efficiency for plasmid-carried ARGs. The absolute abundance of plasmid-carried ARGs in the effluent was reduced by 0.4 to 11 times compared to chromosomal ones, showing removal stability improved by 13.11% to 74.51%. Additionally, the functional microbial community attached on the high porosity of biochar surface promoted ARGs retention, increasing diffusion limitation in microbial assembly mechanisms by 4.61-29.44%, which played a key role in plasmid-mediated horizontal gene transfer (HGT). Partial least squares structural equation modeling (PLS-SEM) revealed that biochar-mediated environmental changes and the HGT of mobile genetic elements (MGEs) were critical factors in reducing plasmid-carried ARGs in EEFs.