Structural organization of diatom pyrenoids in environmental samples

Presented by Manon DEMULDER

Diatoms contribute substantially to global marine carbon fixation, yet the structural basis of this process in natural populations remains poorly characterized. In many algae, carbon fixation occurs within the pyrenoid, a phase-separated chloroplast compartment enriched in Rubisco. While pyrenoid architecture has been studied in laboratory strains, its organization in natural environments is largely unknown.

In the model diatom Thalassiosira pseudonana, we recently identified a protein sheath (PyShell) surrounding the pyrenoid. Disrupting this structure alters pyrenoid morphology, impairs CO₂ fixation, and perturbs thylakoid organization. This highlights the functional importance of pyrenoid architecture.

To investigate pyrenoids in environmental diatom populations, we developed workflows to apply cryo-electron tomography (cryo-ET) directly to environmental samples. Analysis of isolates and mixed communities collected from Icelandic coastal waters reveals unexpected morphological diversity and previously undescribed pyrenoid architectures. These workflows enable structural studies of carbon fixation compartments in natural algal populations and open the possibility to explore how pyrenoid organization varies across ecological niches and environmental stress.