From the realm of the really cool:
Henneguya salminicola is a species related to jellyfish, a multicellular animal that does not need oxygen to live.
H. salminicola is a parasite that lives in fish. It’s harmless to people, but leaves white spots on the fish it infects.
24 February 2020
by Michael Le Page
Breathing oxygen is seen as a fundamental characteristic of multicellular animals, but we have found at least one that can’t do it.
“It has lost the ability to breathe oxygen,” says Dorothee Huchon at Tel Aviv University in Israel. It remains a mystery how this animal, a parasite that infects salmon, gets the energy it needs without oxygen, she says, but it probably steals it from its host.
All plants and animals were thought to use oxygen to generate a fuel called adenosine triphosphate (ATP), which powers cellular processes. The generation of ATP from oxygen takes places in structures called mitochondria.
Each mitochondrion has its own tiny genome that is separate from the main genome in the cell nucleus. But when Huchon and her colleagues sequenced the DNA of Henneguya salminicola, which is related to jellyfish, they thought they had made a mistake because they found no mitochondrial DNA at all.
Further studies confirmed the finding. When the team stained H. salminicola with a blue fluorescent dye that binds to DNA, no DNA was visible in cells outside the nucleus. By contrast, when they stained a closely related parasite, blue dots corresponding to mitochondrial genomes were visible outside the nucleus.
So while the cells of H. salminicola have structures that look like mitochondria, they can’t make the enzymes needed to use oxygen to produce ATP. “These are not true mitochondria,” says Huchon.