Charting the landscape of cytoskeletal diversity in microbial eukaryotes

Microbial eukaryotes remain understudied despite their critical ecological importance, with the exception of a few established models. They are often small, difficult to culture, and resistant to standard labeling and imaging techniques. Here, we use ultrastructure expansion microscopy (U-ExM) to carry out high-resolution volumetric imaging of over 200 cultured planktonic eukaryotes across major lineages. By combining U-ExM with pan- and specific immuno-labeling, we reveal microtubule and centrin-containing elements and assign molecular identities to enigmatic cytoskeletal structures observed previously only by electron microscopy. This comprehensive resource provides a basis for understanding cytoskeletal diversity, phenotypic plasticity, and evolutionary dynamics. Moreover, our approach extends to mixed environmental samples, paving the way for environmental cell biology at ultrastructural resolution-a crucial step toward understanding and protecting ecosystems in the face of accelerating biodiversity loss.