Iñaki Ruiz-Trillo

The origin and the process by which eukaryotic cells arose remains one of the great unanswered questions in biology, with Lynn Margulis’s theories regarding the incorporation of a bacterium that would later become the mitochondrion marking a major turning point. Now, Spanish research carried out by IRB Barcelona and the Barcelona Supercomputing Center challenges this view. Without denying the role of mitochondria, it suggests that the process was longer and more complex than previously thought, stretching over hundreds of thousands of years. At least two other different bacteria contributed to the development of eukaryotic cells, and giant viruses appear to have acted as vehicles for genetic transfer. The findings, published in Nature, suggest a much more protracted and gradual process of exchange between microorganisms.

In the ephemeral pools along the coasts of the Caribbean island of Curaçao lives Choanoeca flexa, a tiny unicellular aquatic organism belonging to the choanoflagellates, important for being close relatives of animals. As the pools evaporate and refill, C. flexa can switch between unicellular and multicellular forms in three different ways: by division, by aggregation, or by combining both, mechanisms that were previously thought to be mutually exclusive. The discovery, published today in Nature, may challenge current understanding of the origins of multicellular life.