The “powerhouse of the cell” is apparently not necessary for animal life

March 1, 2020 1:05 PM

Biologists Discover Animal that Lacks Mitochondrial Genome, Doesn't Need Oxygen to Live (Sci-News): An international team of biologists has discovered that a tiny parasite of salmon called Henneguya salminicola has no mitochondrial genome and thus has lost the ability to perform aerobic respiration. "Aerobic respiration was thought to be ubiquitous in animals, but now we confirmed that this is not the case," Prof. Huchon explains (Science Daily). "Our discovery shows that evolution can go in strange directions. Aerobic respiration is a major source of energy, and yet we found an animal that gave up this critical pathway."

Scientists discover first known animal that doesn't breathe (LiveScience):

While that absence is a biological first, it's weirdly in character for the quirky parasite. Like many parasites from the myxozoa class -- a group of simple, microscopic swimmers distantly related to jellyfish -- H. salminicola may have once looked a lot more like its jelly ancestors but has gradually evolved to have just about none of its multicellular traits.

"They have lost their tissue, their nerve cells, their muscles, everything," study co-author Dorothée Huchon, an evolutionary biologist at Tel Aviv University in Israel, told Live Science. "And now we find they have lost their ability to breathe."

Researchers find an animal without mitochondria (Ars Technica):

So, the function of the mitochondrial remnant remains unclear at this point. But it is possible to speculate how this ended up being the only known animal species without functioning mitochondria. When in fish, the organism takes up residence in the white muscles, which apparently function using anaerobic metabolism. While it's not clear what the second host is, plenty of worm options also live in anaerobic environments. So, it's entirely possible that this organism was spending most of its existence without any oxygen to use for metabolism in the first place. [...]

Does this discovery mean that we should rethink the need for oxygen-based metabolisms as a prerequisite for animal life? Not entirely. It's pretty clear that these organisms would have a hard time surviving without animal hosts to provide many of the things we normally associate with more complicated organisms. So, it's entirely possible that the oxygen-based metabolism enabled by complicated cells remains essential for the origin of animals. It's only after those animals exist that it may be dispensable.

A cnidarian parasite of salmon (Myxozoa: Henneguya) lacks a mitochondrial genome (PNAS abstract)

posted by not_the_water (14 comments total)

Typical of parasites, and an amazing example of the principle.

It must be mostly composed of methods to get past the hosts immune system. Plus reproducing... Do parasites evolve into diseases? Is there a sharp difference between a small parasite and a large disease organism?
posted by clew at 1:28 PM on March 1, 2020

Is there any compelling reason why an organism couldn't breathe, say, nitrogen or hydrogen instead?
posted by grumpybear69 at 2:03 PM on March 1, 2020

It sounds like this animal *does* rely upon respiration - it has simply outsourced respiration to its host.
posted by Mr. Excellent at 3:33 PM on March 1, 2020 [6 favorites]

Is there any compelling reason why an organism couldn't breathe, say, nitrogen or hydrogen instead?

Chemistry. Not to say that an exceptionally creative evolutionary force could not make it happen, but the chemical properties of oxygen make it a really good candidate for the job it does in biology.
posted by jjray at 3:38 PM on March 1, 2020 [4 favorites]

Is there a sharp difference between a small parasite and a large disease organism?

Not really. Parasite infection aka parasitic disease is the term used when the agent is an animal or protozoa, mostly by convention:
Although organisms such as bacteria function as parasites, the usage of the term "parasitic disease" is usually more restricted. .

Also for that matter the line between parasite or parasitoid and predator can get a little blurry as well. The nominal conventional difference is if you take bites out of your prey from the inside or outside, but some times it’s kind of both.
posted by SaltySalticid at 4:17 PM on March 1, 2020 [3 favorites]

This is super cool stuff though. Another fun example of an animal that’s lost a lot is giant tube worms. They have lost their ancestral mouths, no guts, and anuses, getting energy only via endosymbiotic chemoautotrophs. But even they have functional mitochondria.
posted by SaltySalticid at 4:25 PM on March 1, 2020

Is there any compelling reason why an organism couldn't breathe, say, nitrogen or hydrogen instead?

Nitrogen is triple bonded and would take an inordinate amount of energy to break. Oxygen is great for respiration because it has high electronegativity but not too high electron affinity. If it had a higher electron affinity like fluorine it would oxidize all the way down your windpipe. That's why fluorine is a shitty thing to breathe. Oxygen was probably picked by evolution because it's both abundant and can be effectively controlled by using electrons to split the molecules, release energy, and oxidize basically on demand.

but the chemical properties of oxygen make it a really good candidate for the job it does in biology.

That's simultaneously both carbon chauvinistic and mitochondrial chauvinistic. Check your privilege, eukaryote.
posted by Your Childhood Pet Rock at 4:26 PM on March 1, 2020 [25 favorites]

Oxygen is great for respiration because it has high electronegativity but not too high electron affinity.

Please correct this non-chemist but isn’t this why you see bacteria that use sulphur instead of oxygen around volcanic vents at the bottom of the sea floor? Sulphur is right below Oxygen on the periodic table, so it has very similar chemical properties.
posted by Big Al 8000 at 5:43 PM on March 1, 2020

Please correct this non-chemist but isn’t this why you see bacteria that use sulphur instead of oxygen around volcanic vents at the bottom of the sea floor? Sulphur is right below Oxygen on the periodic table, so it has very similar chemical properties.

They actually oxidize hydrogen sulfide using the oxygen in the water.

CO2 + H2O + H2S + O2 -> CH2O + H2SO4

Sulfur reducing organisms (those that "breathe" sulfur by using it as a terminal electron acceptor) will usually use something like:

H2 + SO4 2− + 2H+-> H2S+ 4H2O

Ruminants also have methanogenic bacteria in their guts. They turn the H2 and CO2 from the fermentation of cellulose into methane and water using CO2 as the terminal electron acceptor effectively "breathing" CO2.

4H2 + CO2 -> CH4 + 2H2O

Then you just have fucked up things like Geobacter which can use just about any metal oxide they can lay their hands on as a terminal electron acceptor. They have little pili that are conductive and will effectively "breath" metal oxides and reduce them while oxidizing whatever carbon source you can throw at them. We currently use them to deal with oil spills. Scientists are trying to figure out how to turn this into a biobattery given you can throw just about any carbon source at them and these little bastards will eat it.
posted by Your Childhood Pet Rock at 6:33 PM on March 1, 2020 [12 favorites]

Thank you for that reminder. As a carbon based form of life I find the idea of being turned into a battery by engineered bacteria other than comforting. Once the robot overlords find this out it will be the Matrix.;)
posted by Ignorantsavage at 8:43 PM on March 1, 2020

the mitochondria is (not always) the powerhouse of the cell
posted by LeviQayin at 8:44 PM on March 1, 2020

"Not always" is pretty much the only always in biology.
posted by flabdablet at 8:29 AM on March 2, 2020 [3 favorites]

Hydrogen Oxidising Bacteria

Most sciences consist of exceptions.
posted by thatwhichfalls at 2:16 PM on March 2, 2020

One of the authors lives in my neighborhood. Can’t wait to congratulate him when I see him out walking tomorrow. Thanks for this post!
posted by Knowyournuts at 7:47 PM on March 2, 2020