The combined effect of microplastics and tetracycline on soil microbial communities and ARGs

Microplastics (MPs), due to their difficult degradation and adsorption characteristics, are highly prone to form compound contamination with antibiotic residues in the soil environment, thereby disrupting the soil ecosystem. To address this issue of compound contamination, this study investigated the effects of compound contamination composed of three common MPs-polyethylene (PE), polyamide (PA), and polyvinyl chloride (PVC)-combined with tetracycline(TC), on the structure of soil microbial communities and resistance genes. The results showed that the effects of composite pollution on soil physicochemical properties, enzyme activities, bacterial communities, and antibiotic resistance genes (ARGs) were more significant compared to single-contaminant pollution. Among the composite contaminants, TC combined with PVC and PE significantly increased the absolute abundance of the tetC gene, while the composite contamination of TC with PA had the greatest effect on bacterial diversity. This also increased the relative abundance of the phylum Actinobacteria and significantly affected the relative abundance of the phylum Ascomycetes. In addition, significant correlations were found between soil physicochemical properties, enzyme activities, microbial communities, and ARGs. A positive correlation between the intl1 integrator gene and all target genes suggests that horizontal gene transfer contributes to the enrichment of ARGs. Furthermore, the bacterial genera correlated with ARGs-Ascomycetes, Acidobacteria, Actinobacteria, and Anaplasma-are the major bacterial hosts for ARGs in soil samples. This study provides data to support the investigation of combined microplastic and antibiotic contamination in soil.