LAUSR

Simple Summary Various multicellular animals are currently used as tools for the toxicological assessment of tiny plastic wastes (i.e., microplastics) in aquatic systems. Here, we present Paramecium bursaria as a promising unicellular alternative for evaluating the toxicity of microplastics due to their easy cultivation, low cost, and fewer ethical considerations. We observed a range of behavioral and molecular changes in Paramecium bursaria in response to microplastic exposure. These elicited changes include abnormal swimming patterns, reduced moving speed, impaired predator avoidance, and elevated oxidative stress. Overall, we demonstrated the possibility of using Paramecium bursaria as an alternative eukaryotic species for evaluating the toxicity of microplastics, which may serve as a valuable tool in the study of other environmental contaminants. Abstract Microplastics (MPs) are normally defined as small plastic wastes with a size of 1 μm to 5 mm in diameter. This tiny plastic debris is abundant in aquatic systems and poses a great threat to aquatic biota. To date, toxicological assessment of MPs is predominantly dependent on metazoan animals, although their applications are sometimes limited due to the high cost, narrow ecological niche, or ethical considerations. In this regard, unicellular eukaryotes (i.e., protozoa) that are ubiquitously present in nature represent a promising alternative for evaluating the toxicity of MPs. In this study, we selected Paramecium bursaria (P. bursaria) as a representative of protozoa and further investigated behavioral and molecular changes in MPs-exposed P. bursaria. Our results showed that following MPs uptake, P. bursaria exhibited various changes, including anomalies in swimming patterns, reduction in moving speed, impairment of avoidance behavior, elevation of oxidative stress, and potential disturbance of endosymbiosis. These elicited changes in P. bursaria in response to MPs exposure were pronounced and measurable. Overall, this study demonstrated that P. bursaria could serve as a promising alternative for the toxicological assessment of MPs and may be further applied to evaluate the toxicity of other environmental contaminants.