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Mechanism of Growth Phase-Dependent Nanoplastic Bioaccumulation in Tetrahymena thermophila
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Researchers investigated how the growth phase of the ciliate Tetrahymena thermophila affects the bioaccumulation of polystyrene nanoplastics, finding that exponential-phase cells accumulated significantly more nanoplastics than stationary-phase cells. The results suggest that organism growth state is an important but often overlooked factor in nanoplastic bioaccumulation studies.
Nanoplastics are ubiquitous in aquatic environments, and elucidating their bioaccumulation behavior is essential for assessing toxicity and trophic transfer risks. While most studies focus on nanoplastics properties (e.g., type, size, surface charge), the influence of organismal growth stage remains unclear. Through bioaccumulation kinetic experiments with 10 mg/L polystyrene nanoplastics (PSNPs), this study found that Tetrahymena thermophila (T. thermophila) in the lag phase (cell density 4 × 104 cells/mL) exhibited the highest uptake rate of nanoplastics, 1.2-5.8 times that of the exponential phase (1-5 × 105 cells/mL) and 7.7 times that of the stationary phase (>5 × 105 cells/mL). Lag phase cells also had a larger specific surface area (0.319 vs. 0.271/0.269 μm-1), supporting their heightened uptake capacity. Under PSNP exposure, exponential and stationary phase cells showed significantly elevated reactive oxygen species (ROS) levels, accompanied by downregulated superoxide dismutase (SOD) and stable catalase (CAT) activity, indicating impaired antioxidant defense and potential redirection of energy toward stress mitigation. Consistent with efficient internalization, confocal imaging revealed clear PSNP colocalization within food vacuoles of lag period cells. Proteomic and transcriptomic analysis further confirmed the upregulation of carrier proteins, FAD/FMN oxidoreductases, and pathways associated with cellular components (membrane and organelle membrane) and molecular functions (transporter activity and transmembrane transporter activity) in lag-phase T. thermophila. Collectively, these findings provide a molecular-level understanding of the multi-phase-dependent bioaccumulation of PSNPs, offering critical insights for assessing the environmental risks of polystyrene nanoplastics in dynamic aquatic ecosystems.
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Researchers synthesized polystyrene nanoplastics of four different sizes (50–500 nm) and exposed the ciliated protist Tetrahymena thermophila to each, finding that smaller particles were more toxic and caused greater bioaccumulation, confirming a size-dependent relationship between nanoplastic properties and ecotoxicological risk.
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Researchers found that polystyrene nanoplastics more severely impair the growth, photosynthesis, and metabolism of the marine diatom Chaetoceros neogracile during active cell division than during dormancy, with higher levels of transparent exopolymer particles (sticky gel-like substances) in dormant cultures likely aggregating nanoplastics and reducing their cellular impact.
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Researchers investigated how nanoplastics interact with single-celled organisms called ciliates, which are common in freshwater environments. They found that even at high concentrations, the nanoplastics had minimal toxic effects on the ciliates, but the organisms repackaged and expelled the particles in ways that changed their physical properties. The study suggests that microscopic organisms may play an underappreciated role in transforming nanoplastics and influencing their environmental fate.
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Scientists tracked how a single-celled freshwater organism absorbs and gets rid of microplastics, finding that cells take in plastic particles quickly within the first hour, but levels drop afterward, mostly because the cells divide and "dilute" the plastic between daughter cells rather than actually eliminating it. This matters because these tiny organisms sit at the bottom of the food chain, meaning the microplastics they build up could pass up the chain to fish and eventually to the food we eat, making this research a key step toward understanding how plastic pollution moves through ecosystems and potentially into our diets.
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