They are capable of absorbing other cells.

Falsifiability is one of the pillars of science. If we want to confirm something, someone must be able to prove it is false. When Christian Jogler and his team heard about the discovery of a prokaryotic cell that could “eat” another, they couldn’t believe it.

So they tried to disprove this discovery.

Very abnormal bacteria. In the end, they did the opposite: they provided new evidence and discovered exactly that: a bacterium capable of endocytosis with another cell. That is, a bacterium capable of “eating” another organism.

It seemed impossible. To understand the extraordinary nature of this discovery, it is worth considering some concepts. In biology, there are usually two types of cells: prokaryotes, which are simpler; and eukaryotes, which are more complex. It is from the latter that multicellular life evolved: fungi, plants, and animals have this type of cell. Bacteria, on the other hand, are prokaryotic cells.

Among the key features of this distinction are the cell nucleus and mitochondria. This organelle is responsible for supplying the cell with energy. It is believed that 2,000 million years ago, two prokaryotic cells, an Asgardian archaea and a bacterium, merged, with the bacteria becoming the mitochondria of the other.

It is also believed that this “acquisition” provided the resulting cell with enough energy to carry out the endocytosis process. That is, as we believed, bacteria without mitochondria did not have enough energy to “absorb” other organisms.

Uabimicrobium helgolandensis. The team behind the new analysis looked at a group of bacteria known as planctomycetes. It was already known that these organisms were special in their own way: they were able to “walk” on surfaces or “flow” between other cells, the team explains.

It was while studying this family of bacteria in 2019 that a study pointed to the possibility that bacteria in this family undergo a “phagocytosis-like process,” a finding the team initially set out to disprove.

The opposite happened. While studying a group of planctomycetes discovered in 2014 at Heiligendamm in the Baltic Sea, the team encountered the same behavior. It was in bacteria they called Uabimicrobium helgolandensis.

“Prey” of bacteria. This is the second evidence of the existence of what the team calls “prey bacteria.” A more detailed study of this bacterium, including sequencing its genes, will not only allow us to prove the existence of these bacteria that can eat other cells, but will also help us better understand the molecular mechanisms that allow them to do so. Details of this analysis have been published in a paper in the journal. mBio.

Understanding Eukaryogenesis. Above all, the study could open the door to a better understanding of the processes that led to the emergence of complex life on our planet. In this way, we can imagine what molecular mechanisms allowed for the merging of cells that led to the emergence of eukaryotes billions of years ago.

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Image | University of Jena / Wurzbacher, Hammer et al., 2024