Scientists have found a microbe that does something textbooks say is impossible: It’s acomplex cell that survives without mitochondria.

Mitochondria are the powerhouses inside eukaryotic cells, the type of complicated cellthat makes up people, other critters and plants and fungi. All eukaryotic cells contain anucleus and little organelles — and one of the most famous was the mitochondrion.

“They were considered to be absolutely indispensable components of the eukaryoticcell and the hallmark of the eukaryotic cell,” says Anna Karnkowska, a researcher inevolutionary biology at the University of British Columbia in Vancouver. Karnkowskaand her colleagues describe their new find in a study published online Thursday in thejournal Current Biology.

i

This is a light micrograph of the microbe thatevolutionary biologists say lives just fine without anymitochondria.

Naoji Yubuki/Current Biology

Mitochondria have their own DNA, and scientists believethey were once free-living bacteria that got engulfed byprimitive, ancient cells that were evolving to become thecomplex life forms we know and love today.

For decades, researchers have tried to find eukaryoticcells that don’t have mitochondria — and for a while theythought they’d found some. One example is Giardia, ahuman gut parasite that causes diarrhea. It wasconsidered to be a kind of living fossil because it had anucleus but didn’t seem to have acquired mitochondria.But additional studies on Giardia and other microbesshowed that actually, the mitochondria were there.

“It turned out that all of them actually had some kind ofremnant mitochondrion,” says Karnkowska, who notesthat mitochondria perform key jobs in the cell beyond just generating power.

A biggie is assembling iron-sulfur clusters for certain proteins, which is thought to be amitochondrial function that’s really essential. So even if a microbe powers itself in adifferent way and has a limited form of the organelle that isn’t the same as themitochondria found in people, Karnkowska says, “it’s still a mitochondrion and it hassome important function for the cell.”

That kind of vestigial mitochondrion is what she expected to find when she was aresearcher at Charles University in Prague and started investigating a particular gutmicrobe that had been isolated from a researcher’s pet chinchilla.

After she and her colleagues sequenced the gut microbe’s genome, however, theyfound no trace that it made any mitochondrial proteins at all. “So that’s a greatsurprise for us,” she says. “That should theoretically kill the cell — it shouldn’t exist.”

What they learned is that instead of relying on mitochondria to assemble iron-sulfurclusters, these cells use a different kind of machinery. And it looks like they acquired itfrom bacteria.

The researchers say this is the first example of any eukaryote that completely lacksmitochondria.

Michael Gray, a biochemist at Dalhousie University in Halifax, Nova Scotia, says theresearchers have made a “compelling” case that they have a bona fide eukaryotewithout any vestige of a mitochondrion; he calls the finding “unprecedented.”

“The observation is significant, in that it clearly demonstrates that a eukaryote can stillbe a eukaryote without having a mitochondrion,” he tells Shots via email.

However, the results do not negate the idea that the acquisition of a mitochondrionwas an important and perhaps defining event in the evolution of eukaryotic cells, headds.

That’s because it seems clear that this organism’s ancestors had mitochondria thatwere then lost after the cells acquired their non-mitochondrial system for making iron-sulfur clusters.

“This is not the missing link of eukaryotic evolution,” agrees Mark Van Der Giezen, aresearcher in evolutionary biochemistry at the University of Exeter in the UnitedKingdom.

Still, he says, it is an example of how flexible life is.

“It lives in an area without oxygen and therefore can get rid of a lot of biochemistrythat you and I would need in our cells to survive,” says Van Der Giezen. “Thisorganism managed to adapt in such a way that it could lose an organelle, which everytextbook will tell you is an essential feature of eukaryotes. That’s pretty amazing. Itshows you that life is extremely creative in finding a way to eke out an existence.”