Cell architecture regulates species-specific micro-nanoplastic toxicity through targeted organelle disruption and energetic pathway rewiring in freshwater algae: Insights from deuterium isotope tracing, ultrastructural profiling, and multi-omics.

Micro-nanoplastics (MNPs) are prevalent in aquatic environments, yet the species-specific toxicological mechanisms associated with inherent cellular architecture remain poorly understood. Here we utilized synthesized deuterium (2H) stable isotope-labeled polystyrene MNPs (2H-PSMNPs; 0.1 μm and 2 μm) to quantify cellular uptake in two microalgae with contrasting cell architectures: Chlamydomonas reinhardtii (rigid cell wall) and Euglena gracilis (cell-wall deficient). Exposure at 1 mg/L (environmentally relevant) and 5 mg/L (a mechanistic dose) showed that 2H-PSMNPs inhibited growth in both algal species. Under the most inhibitory treatment, growth inhibition reached approximately 35% in C. reinhardtii and 25% in E. gracilis. Isotope-based quantification revealed that E. gracilis accumulated 32 μg/g dry weight of 0.1 μm 2H-PSNPs, about twice that in C. reinhardtii. Ultrastructural confirmed distinct organelle targeting, revealing mitochondrial damage in C. reinhardtii, whereas E. gracilis suffered pronounced chloroplast disruption. Multi-omic analyses revealed species-specific metabolic reprogramming: C. reinhardtii adapts by reshaping propanoate metabolism and amino acid turnover, whereas E. gracilis suffers disrupted photosynthetic electron transport and oxidative phosphorylation. Structural equation modeling confirmed that species-specific cell traits contribute 67.3% to the overall transcriptomic and metabolic response. These findings link cell architecture to MNP internalization and toxicity, supporting preliminary screening of vulnerable species by cell-wall traits.