What is life without oxygen

Researchers discover the first animal that can live entirely without oxygen

Do you remember which discovery the Nobel Prize for Medicine was awarded for last year? William Kaelin, Gregg Semenza and Sir Peter Ratcliffe were recognized for their ability to decipher how oxygen perception works at the cellular level.

That sounds a bit special, but it is essential for almost all animal life: Oxygen provides the cells with the fuel they need to generate energy. Specifically, the gas is used in the mitochondria - the cells' power stations - to convert the energy-rich components of food into chemical energy that can be used by the cells in the form of the "fuel" adenosine triphosphate (ATP).

First anaerobic multi-cell

Only a few months after receiving the Nobel Prize, researchers working with Dayana Yahalomi (University of Tel Aviv) have now discovered a multicellular living being that does not need functioning mitochondria - and therefore also without aerobic cell respiration and without oxygen. As the team of scientists reports in the journal "PNAS", this eccentric is the tiny fish parasite

The parasite, which belongs to the cnidarians and appears as white nodules in the meat of salmon, is harmless to humans, but it poses considerable problems for salmon farmers. And it is likely to be the first known animal to have given up the basic ability of cells to breathe oxygen, as Yahalomi's colleague Dorothee Huchon explains.

Discovery after sequencing

The researchers explain how this happened because the fish parasite lives mainly in oxygen-poor tissues anyway. Such an adaptation to anaerobic conditions is already known from unicellular organisms such as some amoebas and ciliates. However, as the new discovery shows, it appears to have developed in a multicellular organism as well.

The team made the discovery after sequencing the genome of this salmon parasite. During the analyzes, the researchers noticed that the cells of Henneguya salminicola still contain organelles that look like mitochondria. But unlike real mitochondria, the organelles no longer had their own mitochondrial genome. Most of the genes that are responsible for mitochondrial function are also missing from the cell nucleus DNA.

Mysterious energy generation

The big question that remains is how the salmon parasite gains energy without oxygen and without mitochondria. The researchers have two assumptions: On the one hand, Henneguya salminicola could pull the fuel from the surrounding cells of the fish tissue. On the other hand, it cannot be ruled out that it has an oxygen-free type of breathing - similar to anaerobic protozoa. This hypothesis is supported by the fact that the fish parasite still has organelles and membranes. This could indicate a "misuse" of these organelles.

"Our discovery shows that evolution can take strange paths," sums up Dorothee Huchon. Supplementary studies should now show how the unique parasite meets its energy needs in this strange way. (Klaus Taschwer, February 27, 2020)