An international team of scientists —including Jone Bilbao, Estibalitz Txurruka and Sergio Seoane of the EHU— has managed to observe the internal architecture of over 200 marine microeukaryotes in unprecedented detail. The study was published recently in the journal Cell and uses samples from the EHU’s Basque Microalgae Culture Collection (BMCC), thus demonstrating how the resources available in the collection can be used in cutting-edge international research.

“Microeukaryotes are tiny, single-celled organisms that form part of plankton and perform essential functions in the oceans: they produce oxygen, form the basis of food webs, and regulate core ecological processes. Despite their importance, their small size and brittle nature have largely kept them out of the reach of science,” said Sergio Seoane, lecturer and researcher in the EHU’s department of Plant Biology and Ecology.

Applying Ultrastructure Expansion Microscopy (U-ExM) is the innovative technique used that allows cells to be physically “expanded”, thus increasing their size without destroying their structure, and this is combined with specific markers that reveal proteins and internal elements. “This makes it possible to observe their cellular architecture in three dimensions with a level of detail that could previously only be achieved with electron microscopy, but in a much broader and more systematic way,” explained Seoane.

This technique enabled the researchers to analyse more than 200 species of microeukaryotes, including green algae, dinoflagellates, haptophytes, ciliates, euglenoids and cryptophytes. “We managed to identify unique internal structures of the cytoskeleton —microtubules, filaments, and centrioles— and gain a detailed understanding of how these structures function, thus completing an unprecedented map of the cell diversity of these organisms,” said Jone Bilbao, a Post-PhD researcher in the EHU's Department of Plant Biology and Ecology.

A scale change for marine biology

The finding is not restricted to the lab. U-ExM can also be applied to environmental samples collected directly from the ocean, thereby offering a more realistic view of how these creatures live in their natural ecosystems. “This constitutes a scale change in marine biology: it allows us to move from studying organisms in culture to observing microscopic life in its actual context, with direct implications for understanding the functioning and resilience of ecosystems in the face of climate change and biodiversity loss,” as Estibalitz Txurruka, a post-PhD researcher in the EHU’s Department of Plant Biology and Ecology, pointed out.

Understanding the cellular architecture of these microorganisms is “key” not only for basic biology, but also for environmental protection. “Each internal structure reveals how organisms adapt, move around and survive, and how their proper functioning sustains ecological networks that are essential for life on the planet,” Seoane explained.