Deciphering the role of polyethylene microplastics on antibiotic resistance genes and mobile genetic elements fate in sludge thermophilic anaerobic digestion process

The retention of microplastics in sewage sludge, a reservoir of antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs), has attracted increasing attention. However, the impact of polyethylene microplastics (PE-MP) on the fate of ARGs and MGEs is far from fully understood in sewage sludge's thermophilic anaerobic digestion process (AD). The present study demonstrated that PE-MP with the size of 40-48 mu m at concentrations of 50, 100, and 200 particles/g-TS could enlarge total ARGs abundance. Meanwhile, a significant positive (r = 0.96, p < 0.05) correlation was observed between PE-MP concentration and total MGEs content. Microbial analysis revealed the enrichment of some functional genus under the stress of PE-MP, which might be the po-tential host of ARGs and MGEs. The relative abundance of acetogens Thermoanaerobacter increased from 27.60 % to 32.80 % and hydrolytic bacteria Caldicoprobacter enriched by 28.03 % when PE-MP content increased from zero to 200 particles/g-TS. The potential hosts were subsequently identified through co-occurrence networks, some of which were identified as pathogens. Strong positive correlations between PE-MP, ARGs, and MGEs were observed using redundancy analysis and correlation analysis. Additionally, the structural equation model indi-cated the direct and indirect influence of PE-MP on the abundance of ARGs and MGEs. MGEs could enhance the acquisition and dissemination of ARGs directly. Taking together, our findings deciphered the contribution of PE -MP to the spread of ARGs and MGEs in the sludge AD process, which might pose risks to human health and should be considered during sewage sludge disposal.

Automated summary

This study revealed the impact of polyethylene microplastics (PE-MP) on the abundance of antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) in sewage sludge. Microbiological analysis identified potential hosts enriched under the stress of PE-MP. The results showed that PE-MP had both direct and indirect effects on the abundance of ARGs and MGEs.