Adsorbed Sulfamethoxazole Exacerbates the Effects of Polystyrene (∼2 μm) on Gut Microbiota and the Antibiotic Resistome of a Soil Collembolan

Microplastics pollution in the environment is now receiving worldwide attention; however, the effects of copollution of antibiotics and microplastics on the gut microbiome of globally distributed and functionally important nontarget soil animals remain poorly understood. We studied a model collembolan (<i>Folsomia candida</i>) and found that the ingestion of microplastics (polystyrene, 2-2.9 μm) substantially altered the gut microbiome, antibiotic resistance gene (ARG) profile, and the isotopic fractionation in the soil collembolan tissue. Importantly, collembolans exposed to polystyrene microplastics loaded with sulfamethoxazole (MA) presented a distinctive gut microbiome, ARG profile, and isotopic fractionation compared to those exposed to polystyrene alone (MH). We observed that the abundance of ARGs and mobile genetic elements (MGEs) in the MA-treated collembolan guts was significantly higher than in the MH and the control treatments. There were also strong interactions between the gut microbiome and ARGs in the collembolan guts. We further found that bacterial β-diversity correlated significantly with the δ¹³C and δ¹⁵N values in collembolan body tissues. Together, our results indicate that changes in isotopic fractionation and ARG profiles in the collembolan were induced by the changes in gut microbiota and suggest that microplastics from diverse sources may have profound influences on soil fauna and soil food webs.