Earthworms restructure the distribution of extracellular antibiotics resistance genes of sludge by modifying the structure of extracellular polymeric substances during vermicomposting

Abstract

The role of earthworms in reducing the antibiotic resistance genes (ARGs) in sludge vermicompost remains unclear. The structure of extracellular polymeric substance (EPS) of sludge may be associated with the horizontal gene transfer behavior of ARGs in the vermicomposting of sludge. Therefore, this study aimed to investigate the effects of earthworms on the structural characteristics of EPS associated with the fate of ARGs in EPS during the vermicomposting of sludge. The results showed vermicomposting could diminish the abundance of ARGs and mobile genetic elements (MGEs) in the EPS of sludge by 47.93 % and 7.75 %, compared to the control, respectively. Relative to the control, vermicomposting also led to the reduction of MGEs abundances in the soluble EPS of 40.04 %, lightly bound EPS of 43.53 %, and tightly bound EPS of 70.49 %, respectively. The total abundances of certain ARGs dramatically diminished 95.37 % in tightly bound EPS of sludge during vermicomposting. In vermicomposting, the main influencing factor of ARGs distribution was the proteins in LB-EPS, accounting for 48.5 % of the variation. This study suggests that the earthworms lower the total abundances of ARGs by regulating the microbial community and modifying the microbial metabolic pathways associated with ARGs and MGEs in the EPS of sludge.