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Polystyrene microplastics impact the occurrence of antibiotic resistance genes in earthworms by size-dependent toxic effects
Summary
Researchers exposed earthworms to polystyrene microplastics of different sizes in soil and found that 10-micrometer particles at low concentrations led to the highest abundance of antibiotic resistance genes. The microplastics caused toxicity that altered gut microbial communities, changing the microenvironment and favoring bacteria carrying resistance genes. The study highlights that microplastic size plays a critical role in driving the spread of antibiotic resistance in terrestrial environments.
Microplastics (MPs) and antibiotic resistance genes (ARGs) are two classes of emerging and prevalent contaminants in terrestrial environments. To date, effects of MPs on the occurrence of ARGs in terrestrial invertebrates remain uncertain. Here we exposed earthworms to a soil amended with polystyrene MPs at two environmentally relevant concentrations to elucidate the occurrence and mechanisms of ARGs in earthworms impacted by MPs with different sizes. Nano-size and 10 mg/kg of 100 µm MPs slightly affected the occurrence of ARGs in earthworms. Highest abundance of ARGs was found in the presence of 10 mg/kg of 10 µm MPs, whereas 100 mg/kg of 10 µm MPs significantly changed the profile of ARGs. Metagenomics sequencing and toxicity tests indicated that MPs caused toxicity and influenced the abundance of microbial community in earthworms, resulting in the changes of ARGs. Results of proteomics and metabolomics demonstrated that 100 mg/kg of 10 µm MPs changed the microenvironment of earthworm gut, built a new homeostatic process, and thus increased the abundance of key bacterial that carried a variety of ARGs. This study highlights the size-dependent toxic effects of MPs and their impacts on the transfer of ARGs in terrestrial environments.