First non-oxygen breathing animal discovered.

[The Romulan Republic]

https://sciencedaily.com/releases/2020/ ... 114408.htm

Researchers at Tel Aviv University (TAU) have discovered a non-oxygen breathing animal. The unexpected finding changes one of science's assumptions about the animal world.

A study on the finding was published on February 25 in the Proceedings of the National Academy of Sciences by TAU researchers led by Prof. Dorothee Huchon of the School of Zoology at TAU's Faculty of Life Sciences and Steinhardt Museum of Natural History.

The tiny, less than 10-celled parasite Henneguya salminicola lives in salmon muscle. As it evolved, the animal, which is a myxozoan relative of jellyfish and corals, gave up breathing and consuming oxygen to produce energy.

"Aerobic respiration was thought to be ubiquitous in animals, but now we confirmed that this is not the case," Prof. Huchon explains. "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."

Some other organisms like fungi, amoebas or ciliate lineages in anaerobic environments have lost the ability to breathe over time. The new study demonstrates that the same can happen to an animal -- possibly because the parasite happens to live in an anaerobic environment.

Its genome was sequenced, along with those of other myxozoan fish parasites, as part of research supported by the U.S.-Israel Binational Science Foundation and conducted with Prof. Paulyn Cartwright of the University of Kansas, and Prof. Jerri Bartholomew and Dr. Stephen Atkinson of Oregon State University.

The parasite's anaerobic nature was an accidental discovery. While assembling the Henneguya genome, Prof. Huchon found that it did not include a mitochondrial genome. The mitochondria is the powerhouse of the cell where oxygen is captured to make energy, so its absence indicated that the animal was not breathing oxygen.

Until the new discovery, there was debate regarding the possibility that organisms belonging to the animal kingdom could survive in anaerobic environments. The assumption that all animals are breathing oxygen was based, among other things, on the fact that animals are multicellular, highly developed organisms, which first appeared on Earth when oxygen levels rose.

"It's not yet clear to us how the parasite generates energy," Prof. Huchon says. "It may be drawing it from the surrounding fish cells, or it may have a different type of respiration such as oxygen-free breathing, which typically characterizes anaerobic non-animal organisms."

According to Prof. Huchon, the discovery bears enormous significance for evolutionary research.

"It is generally thought that during evolution, organisms become more and more complex, and that simple single-celled or few-celled organisms are the ancestors of complex organisms," she concludes. "But here, right before us, is an animal whose evolutionary process is the opposite. Living in an oxygen-free environment, it has shed unnecessary genes responsible for aerobic respiration and become an even simpler organism."

I'm particularly interested in the implications for exobiology.

[chimericoncogene]

I want to know how the blasted thing evolved, and what the selection pressures were. Very few eukaryotes, IRRC, have managed to get rid of their mitochondrial slaves.

[Broomstick]

There was an earlier thread (which I can't seem to locate this morning) about another multi-cellular non-oxygen despondent critter found a few years ago, which would make this animal number two. The first one lives in marine sediment and was discovered back around 2010, which might be why it's not remembered. Here's a link to an article about it

[Broomstick]

I want to know how the blasted thing evolved, and what the selection pressures were. Very few eukaryotes, IRRC, have managed to get rid of their mitochondrial slaves.

It's a parasite, and as a general rule vertebrates don't have a lot of spare oxygen floating around free inside them. All vertebrate parasites have to deal with low oxygen environments.

[chimericoncogene]

It's a parasite, and as a general rule vertebrates don't have a lot of spare oxygen floating around free inside them. All vertebrate parasites have to deal with low oxygen environments.

Correct me if I'm wrong, but I recall that vertebrates have to have a high partial pressure of oxygen inside them for their cells to live. They have a lot of spare oxygen, with huge safety margins (well, at least people and I presume mammals do).

Hemoglobin's affinity for oxygen falls dramatically in low-oxygen environments - if this mechanism breaks down, as it does in CO poisoning, which locks the hemoglobin in a high affinity state, thus worsening oxygen transport in addition to occupying hemoglobin slots, you tend to get very ill. Any low oxygen environment should rapidly become oxygenated.

Does it live in necrotic tissue or the gut or something?

[Jub]

Correct me if I'm wrong, but I recall that vertebrates have to have a high partial pressure of oxygen inside them for their cells to live. They have a lot of spare oxygen, with huge safety margins (well, at least people and I presume mammals do).

Hemoglobin's affinity for oxygen falls dramatically in low-oxygen environments - if this mechanism breaks down, as it does in CO poisoning, which locks the hemoglobin in a high affinity state, thus worsening oxygen transport in addition to occupying hemoglobin slots, you tend to get very ill. Any low oxygen environment should rapidly become oxygenated.

Does it live in necrotic tissue or the gut or something?

I think, and this is literally just uneducated supposition, that the key point of distinction here is that the oxygen is securely tucked away inside cells/tissues. As an example, I could drop you into an airless vat of highly oxygenated blood and I can tell you that you would not end up in a highly oxygenated state.

Of course this can, and often does, break down at the scales these critters live at and even if they didn't it wouldn't surprise me if things could adapt to steal the oxygen they need from nearby cells.

[chimericoncogene]

I think, and this is literally just uneducated supposition, that the key point of distinction here is that the oxygen is securely tucked away inside cells/tissues. As an example, I could drop you into an airless vat of highly oxygenated blood and I can tell you that you would not end up in a highly oxygenated state.

Of course this can, and often does, break down at the scales these critters live at and even if they didn't it wouldn't surprise me if things could adapt to steal the oxygen they need from nearby cells.

If you were the size of a few cells (or maybe even a roundworm, or even a tapeworm) and your skin were permeable to oxygen, then yes, you would end up in a highly oxygenated state. You don't because you are too big, with a miniscule surface area, and because your skin isn't exactly permeable.

There is literally something called the oxygen binding curve. If the ppO2 is low, Hb will release oxygen, so the ppO2 and Hb saturation will usually match.

[Jub]

If you were the size of a few cells (or maybe even a roundworm, or even a tapeworm) and your skin were permeable to oxygen, then yes, you would end up in a highly oxygenated state. You don't because you are too big, with a miniscule surface area, and because your skin isn't exactly permeable.

There is literally something called the oxygen binding curve. If the ppO2 is low, Hb will release oxygen, so the ppO2 and Hb saturation will usually match.

I know that this is the case for a cell in, for example, oxygenated water. Is that still the case where there isn't a convenient medium for oxygen transport such as being pressed between muscle fibers?

[chimericoncogene]

I know that this is the case for a cell in, for example, oxygenated water. Is that still the case where there isn't a convenient medium for oxygen transport such as being pressed between muscle fibers?

You do realize there is something called tissue fluid, right? Beyond the bloodstream, oxygen transport is primarily by diffusion of dissolved oxygen.
Also, blood is fifty percent plasma. Five percent of the body's oxygen or so is transported in blood plasma as dissolved oxygen.

[Jub]

You do realize there is something called tissue fluid, right? Beyond the bloodstream, oxygen transport is primarily by diffusion of dissolved oxygen.
Also, blood is fifty percent plasma. Five percent of the body's oxygen or so is transported in blood plasma as dissolved oxygen.

Dude, my first post in the thread was an admission that I don't have a deep knowledge of this subject. I asked a question about a scenario where I, a layman, thought there may not be much free oxygen. There's no need to go on the attack.

[chimericoncogene]

Dude, my first post in the thread was an admission that I don't have a deep knowledge of this subject. I asked a question about a scenario where I, a layman, thought there may not be much free oxygen. There's no need to go on the attack.

I understand. Nonetheless, what I have discussed is maybe high-school biology stuff - it's nothing fancy. This stuff is at a level of biology akin to understanding on a basic level how an orbit works in physics, or how O'Neil cylinders keep people on the floor.
My understanding of the subject, too, is limited, which is why my explanations are incomplete. I am not seeing the full picture.

[Jub]

Dude, my first post in the thread was an admission that I don't have a deep knowledge of this subject. I asked a question about a scenario where I, a layman, thought there may not be much free oxygen. There's no need to go on the attack.

I understand. Nonetheless, what I have discussed is maybe high-school biology stuff - it's nothing fancy. This stuff is at a level of biology akin to understanding on a basic level how an orbit works in physics, or how O'Neil cylinders keep people on the floor.
My understanding of the subject, too, is limited, which is why my explanations are incomplete. I am not seeing the full picture.

I took physics in high school. There was some biology covered in my grade 10 science class, but that would have been sometime in '03 or '04 and I haven't had much use for said science knowledge since then. I follow along where I can but for obvious reasons that tends to leave holes in one's knowledge base. So please forgive my questions as I'm just throwing out my layman's ideas and seeing if they have any bearing on reality.

[Broomstick]

It's a parasite, and as a general rule vertebrates don't have a lot of spare oxygen floating around free inside them. All vertebrate parasites have to deal with low oxygen environments.

Correct me if I'm wrong, but I recall that vertebrates have to have a high partial pressure of oxygen inside them for their cells to live. They have a lot of spare oxygen, with huge safety margins (well, at least people and I presume mammals do).

Yes... INSIDE their cells, not in the spaces between. And the oxygen is bound up in various ways, not floating free. Oxygen is highly reactive and toxic to many biological processes, even if mitochondrion and energy generation requires it. It has to be kept under careful and strict control.

[chimericoncogene]

Yes... INSIDE their cells, not in the spaces between. And the oxygen is bound up in various ways, not floating free. Oxygen is highly reactive and toxic to many biological processes, even if mitochondrion and energy generation requires it. It has to be kept under careful and strict control.

As I recall, once it is transported to the target capillary beds in hemoglobin in RBCs, oxygen dissociates from the Hb and becomes a dissolved gas, the concentration of which is measured in terms of a partial pressure. Subsequently, oxygen diffuses across cell membranes, through the tissue fluid, and into cells that require oxygen. No active transport proteins are present in this process. I am reasonably sure of this.

The dissolved oxygen is not much - a few percent of what was in the blood - but its concentration is kept constant by a continuous influx of fresh oxygenated hemoglobin. This is a level adequate for normal cellular function and should also be adequate for normal parasitic function, assuming parasitic worms are not so prodigous as to have more biomass than your own muscles.



https://courses.lumenlearning.com/suny- ... o-content/

Myoglobin can bind oxygen, but IRRC its main role is to provide a buffer of oxygen for sudden increases in demand e.g. the first few seconds of running, right after ATP stores are used up but before the lungs and heart can push extra oxygen into the tissues.

The ROS that result from oxygen-using processes in cells are extensively counteracted by cellular repair mechanisms and production of antioxidants like glutathione by various enzymes.

I can't get to the article behind a paywall. As to why there are no mitochondria in this parasite, various sites seem to believe that the answer is the same one as to why tapeworms no longer have digestive systems: they don't need them (tapeworms more or less soak in predigested gut juice laden with nutrients). They grab everything directly from the host, somehow, apparently, including ATP. All they need is a genome which maintains their ability to spread; everything else can be sacrificed to make more genomic material and parasite-spreading gear in the interests of economy. As to whether their larval stages have mitochondria - well, I dunno.

[chimericoncogene]

Fish, of course, may be different, but since a human body is a spacesuit for a fish, I don't think these differences on this level will be too substantial.

EDIT: the abstract notes that the hypoxic environment is a key selection pressure. Apparently, the parasite gets stuck in a bunch of cysts inside the infected salmon, which I presume can be very hypoxic environments when filled with necrotic tissue and debris.

EDIT EDIT: BINGO! Parasitic cysts tend to be hypoxic environments.

[chimericoncogene]

EDIT EDIT: BINGO! Parasitic cysts tend to be hypoxic environments.

A cyst is basically the result of chronic inflammatory responses to foreign bodies/harmful organisms. The body encrusts the bad thing in lots and lots of fibroblasts (structural walling cells) and white blood cells (neutrophils are equipped for hypoxic necrotic tissue, - lots of anaerobic respiration in them - so they still work a little less well), and just lets the thing fester. It's what tubercules in TB are, and why you can see capsules around benign tumors. Cystercercosis is what happens when you eat tapeworm eggs, and the tapeworm things you're a pig. You get these necrotic cysts in your muscles and brain, which can cause all sorts of problems (seizures and stuff, IRRC).



Cysts in salmon meat. Not as much oxygen in those white things.

[B5B7]

If this thing consists of only ten cells can it be truly classified as an animal?

[Broomstick]

Yep.