Complex Bilateral Interactions Determine the Fate of PolystyreneMicro- and Nanoplastics and Soil Protists: Implications from a Soil Amoeba

:nano- and microplastics have become a seriousglobal concern, threatening our living environments. Previousstudies have shown that many organisms, including bacteria,animals, and plants, can be affected by microplastics. However,little is known about one ecologically important group of soilorganisms, the protists. In this study, we investigated howpolystyrene micro- and nanoplastics interacted with a soil amoebaDictyostelium discoideum. The results showed that environmentalconcentrations of nano- and microplastics could negatively affectthe soil amoeba'sfitness and development.D. discoideumingestedboth nano- and microplastics through phagocytosis but packed andexcreted them during slug migration, which also promoted theirbiodegradation. Fourier transform infrared spectroscopy analyses revealed the formation of new oxygen-containing functional groupsand the sign of possible oxidation of polystyrene. Also, nano- and microplastic exposure disrupted the nutrient and energymetabolisms ofD. discoideumand affected the expression of key genes (e.g.,cf45-1,dcsA,aprA,dymB, andgef B) related tomorphogenesis and phagocytosis. In conclusion, our results show that nano- and microplastics have complex bilateral interactionswith the soil amoeba, affecting each other's fate in the soil environment. This study provides new insights into how soil protistsinteract with nano- and microplastics in the soil ecosystem