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Microplastic Beads Incorporated into a Single Cell ： Analyses Using the Green Paramecium, Paramecium bursaria
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Scientists found that a tiny single-celled organism can absorb microplastic beads directly into its main cell body, not just its "stomach" (food vacuole), meaning the plastic escapes normal digestion and lodges deeper inside the cell. This matters because it shows microplastics may be able to slip past biological barriers designed to keep foreign particles contained, raising questions about how these plastics might behave once inside the cells of larger organisms, including humans.
The unicellular protist Paramecium bursaria harbors hundreds of symbiotic algae resembling Chlorella species in the cell. It is thought that the host P. bursaria uses some of photosynthetic products from these algae when sunlight is available. When photosynthesis cannot be performed, P. bursaria preys on bacteria, molds, algae, etc. in the surroundings for an energy source. Interestingly, some of the algae were observed to move from the food vacuole to the cytoplasm, becoming symbionts, within several days after incorporation into the cell. Since P. bursaria is benthic, it should be possible for various kinds of precipitated tiny particles to be taken up into the cell body during predation. In this study, microplastic (MP) beads with a diameter of 1 μm, which is about the same size as the algae, were mixed in the suspension medium of P. bursaria . It was observed that uptake of the beads into the cell body of P. bursaria started within 5 min after mixing, and the beads were observed inside P. bursaria even several days after the addition to the P. bursaria culture suspension. It is highly probable that the MP beads observed in the cell body somehow escaped from the food vacuole and moved into the cytoplasm.
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Paramecium bursaria as a Potential Tool for Evaluation of Microplastics Toxicity
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The ciliate protozoan Paramecium bursaria was evaluated as a novel model organism for microplastic toxicity testing, showing dose-dependent adverse effects from microplastic exposure at concentrations relevant to aquatic environments. The authors propose P. bursaria as a useful complement to metazoan test organisms for early-tier ecotoxicological screening.
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