Mixture Effects of Polystyrene Microplastics on the Gut Microbiota in C57BL/6 Mice

Microplastics are plastic particles with sizes of less than 5 mm. The ubiquity of microplastics in the environment has raised serious public health concerns. Microplastics could disturb the composition of the gut microbiota due to both chemical composition and physical interactions, which might further influence the metabolism and immune function of the host. However, most of the exposure studies chose microplastics of specific sizes. In the natural environment, living organisms are exposed to a mixture of microplastics of various sizes. In this study, male C57BL/6 mice were exposed to polystyrene (PS) microplastics with different sizes, including microplastics with diameters of 0.05-0.1 μm (PS0.1 group, 100 ppb), 9-10 μm (PS10 group, 100 ppb), and microplastic mixtures of both 0.05-0.1 and 9-10 μm (PSMix group) at a total concentration of 100 ppb (50 ppb for each size). Mixture effects of microplastics were investigated on the composition of bacteria and fungi as well as functional metagenome and microbial genes encoding antibiotic resistance and virulence factors. We found that some bacteria, fungi, and microbial metabolic pathways were only altered in the PSMix group, not in the PS0.1 or PS10 group, suggesting the toxic effects of the microplastic mixture on the composition of fungi and bacteria, and the functional metagenome is different from the effects of microplastics at specific sizes. Meanwhile, altered genes encoding antibiotic resistance and virulence factors in the PSMix group were shared with the PS0.1 and PS10 groups, possibly due to functional redundancy. Our findings help improve the understanding of the toxic effects of the microplastic mixture on the gut microbiome.