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Comment by hammock | Hacker News Reader

>The complete absence of mitochondria is a secondary loss, not an ancestral feature

Basically the organism evolves to not need its mitochondria, replacing it with a different system.

The story goes that mitochondria used to be separate organisms (they have their own DNA) living in symbiosis with other cells, and eventually being subsumed.

So this would be an example of an organism similarly evolving to incorporate a bacterial symbiotic relationship (as opposed to what the mitochondria provide). Not surprising to me that this is possible, or that we eventually found something like this, given that this is how mitochondria came to exist in cells to begin with.

I was hoping that we would have found an organism that existed before mitochondria were subsumed into cells. That would be cool

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Exactly. This is by far the first eukaryote known without mitochondria -- the classic case is Giardia, but like this organism it is clear that it lost them rather than being a relic of the age before endosymbiosis.

To be clear, this is a lateral gene transfer from bacteria, which doesn't necessitate previous a symbiotic relationship with that bacteria, right?

Mitochondria are self-contained organelles. Gene transfer would be if their DNA became part of the nuclear DNA. What you suggest is that there was first a lateral transfer, and then that transferred DNA was ejected from the nucleus, and the cell somehow formed organelles that look surprisingly like bacteria. The theory I believe is that symbiosis evolved into mutual dependency, with the mitochondria starting to live inside the cells instead of outside them sometime along the way.

I wouldn't be so sure of that part of the finding, assessing lateral gene transfer is extremely difficult - consider the situation of the tardigrade.

It might just be that any such organism was almost immediately out-competed by anything with an internal chemical energy factory, so we never will.

IIRC, mitochondria are only used for aerobic respiration (which requires oxygen). So there might be a chance for such an organism to have survived an an anaerobic/oxygen-free environment.

That's a good point, you're right it's definitely oxygen dependent (the electron transport chain just won't work without it). Given the interest in various extremophiles, I think that if it exists we'll find it sooner or later.

"I was hoping that we would have found an organism that existed before mitochondria were subsumed into cells. That would be cool"

Wait - isn't that what archaea is ?

Archaea are prokaryotes, not eukaryotes

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