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Scientists Find Gut Microbe That Survives Without Mitochondria (npr.org)
An anonymous reader writes: Scientists have found a eukaryote microbe that completely lacks mitochondria, which are the powerhouses inside eukaryotic cells, the type of cells that make up humans, animals, plants and fungi. All eukaryotic cells contain a nucleus, organelles and mitochondrion. Scientists believe they were once free-living bacteria that got engulfed by primitive, ancient cells that were evolving to become what they are today. Anna Karnkowska, a researcher in evolutionary biology at the University of British Columbia in Vancouver, found a gut microbe that contains no trace that it made any mitochondrial proteins at all. "That should theoretically kill the cell -- it shouldn't exist," she said. The researchers learned that these cells use a kind of machinery that is different than relying on mitochondria to assemble iron-sulfur clusters, which is thought to be a mitochondrial function. Michael Gray, biochemist at Dalhousie University in Halifax, Nova Scotia, calls the discovery of a eukaryote without any vestige of mitochondrion, "unprecedented." He adds, the results do not negate the idea that the acquisition of a mitochondrion was an important and perhaps defining event in the evolution of eukaryotic cells, because this organism's ancestors had mitochondria that were then lost after the cells acquired their non-mitochondrial system for making iron-sulfur clusters.
Agreed. As I recall one of the potential attack vectors against most cancers is the fact that energy production moves from the mitochondria to the cytoplasm. So it would seem at least naively obvious that even human cells have the genetic capacity to survive without mitochondria (assuming they serve no other essential function), that other eukaryotes can do so as well should be no surprise.
That makes the interesting question, how did microbes lose them? Or are they descended from per-mitochondrial eukaryotes? And even, if we're feeling tangential, why are mitochondria so common in the first place?
--- Most topics have many sides worth arguing, allow me to take one opposite you.
This was my understanding, but TFA says:
For decades, researchers have tried to find eukaryotic cells that don't have mitochondria --- and for a while they thought they'd found some. One example is Giardia, a human gut parasite that causes diarrhea. It was considered to be a kind of living fossil because it had a nucleus but didn't seem to have acquired mitochondria. But additional studies on Giardia and other microbes showed that actually, the mitochondria were there.
"It turned out that all of them actually had some kind of remnant mitochondrion," says Karnkowska, who notes that mitochondria perform key jobs in the cell beyond just generating power.
I figure their knowledge is more compete and up to date than mine.
Quattuor res in hoc mundo sanctae sunt: libri, liberi, libertas et liberalitas.
Mitosomes in Giardia, Entamoeba, and Microsporidia represent the most extreme cases of mitochondrial reduction known to date, and yet they still contain recognizable mitochondrial protein translocases and usually an ISC system. The specific absence of all these mitochondrial proteins in the genome of Monocercomonoides sp. indicates that this eukaryote has dispensed with the mitochondrial compartment completely.