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.

Comments

Mitochondria?

[DarkSabreLord]

Repeat after me: "Mitochondria is not necessarily the powerhouse of the cell"

Re:Mitochondria?

[Immerman]

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?

Re:Mitochondria?

[hyades1]

I think I saw a pron once where some girl rode a Golgi Apparatus until she suffered what appeared to be a grand mal seizure.

Re:Mitochondria?

[jandersen]

I don't really have the time to look things up properly, but if I remember correctly, the mitochrondria are only responsible for the kind of energy production that requires oxygen, and all eukaryotes still have the capacity to use fermentation to some extent. It is far less efficient, which is one of the main reasons why acquiring mitochondria was such a huge leap forward for life. We can experience the process when our muscles need energy faster than our blood is able to deliver the necessary oxygen: lactic acid accumulates, and the muscles start telling the brain to stop it.

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?

The last question is obvious, in a sense: mitochrondria are the most efficient design that has evolved so far, so the cells that have them are superior to all the ones that had another design. As to why this design is actually better - that is lined up for a Nobel Price, I suspect.

Maybe they didn't lose them - I think there is another, possible explanation. The question is whether eukaryotes arose gradually, acquiring mitochondria slightly later in the process, or were they the result of the sudden (in evolutionary terms) inclusion of a bacterium, which could produce ATP or something similar, and which would be able to cooperate with it's host cell? My bets are on the gradual process: microbes learned long ago to live in biofilms, which are surprisingly intimate communities. In this environment they may have learned to copperate, exchanging useful chemicals, becoming symbiotes. Initially living as individual cells, but things like cell nucleus, endoplasmatic reticulum etc could have evolved as structures that served some useful functions in a close knit community like this, and mitochondria could have been a species of bacteria that exchanged ATP or a precursor with something else, which turned out to be so useful that it got invited inside, so to speak. The ability to produce energy by oxidation would probably have released so much energy that it would be far too much to be an advantage to a single bacterial cell, but could have given a major advantage to a biofilm community. Only speculation, of course, since I don't have the means to test the hypothesis.

Good!

[HideyoshiJP]

This is good news. Finally, life has found a way to prevent a real Parasite Eve situation. Let's hope the mitochondria in existing life forms doesn't revolt.

Not all eukaryota have mitochondria

[Anonymous Coward]

Yet again, hyperbole trumps facts. The fringes of the eukaryota portion of the tree of life include anaerobic single celled organisms which do not have mitochondria any more, although their ancestors did. Parabasilids, which include the human pathogen Trichomonas vaginalis, are eukaryotes, are anaerobic, and yet are free of mitochondria. This NPR article is pretty much clickbait.

Re:Not all eukaryota have mitochondria

[Michael Woodhams]

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.

Re:Not all eukaryota have mitochondria

[postglock]

Mitosomes and the hydrogenosomes of Trichomonas vaginalis are degenerate mitochondria. They address this in TFA. This paper reports the new discovery of eukaryotes with no trace of mitochondria at all. From the paper:

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.

It had to be said

[SuperKendall]

Scientists have found a eukaryote microbe that completely lacks mitochondria

The force is weak with this one.

Re:who cares?

[dsmatthews9379]

It means that we can expect to be able to create synthetic cells that have simpler energy systems and those systems could be exotic so that the cells could not survive outside of the laboratory. So this knowledge does in fact contain a very important insight that may profoundly effect how safely and cheaply we can make all forms of biological molecules, including drugs, on an industrial scale.

Re: who cares?

[JustAnotherOldGuy]

Lots of science research has no immediate or apparent value, but may lead to something that does. It adds to the sum of human knowledge, which is usually a good thing.

By the way, stop rubbing those two sticks together, it's a waste of time that won't lead to anything. And that round "wheel" thing those eggheads came up with will never find a use, mark my words.