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  • [♪ INTRO]

  • Oxygen is pretty great stuff.

  • On a chilly morning in the mountains,

  • there's nothing better than breathing a couple of lungs full of fresh O2, right?

  • But some organisms couldn't care less about oxygen.

  • In fact, in 2021, scientists announced the discovery

  • of an organism, distantly related to us, that breathes nitrogen.

  • But that's not all.

  • This single-celled critter offers a window into how the type of cells

  • that make up our bodies

  • may have evolved billions of years ago.

  • Our bodies are constructed from eukaryotic cells

  • a complex cell that contains a central pocket called a nucleus.

  • And because we're made of eukaryotic cells, we're classified as eukaryotes,

  • which is that big, noisy family that includes us, other animals,

  • plants and fungi, plus a few others.

  • The eukaryotes evolved a little under 2 billion years ago.

  • Back then, days were four hours shorter, continents were just becoming a thing,

  • and the population consisted largely of sunlight-eating,

  • oxygen-farting cyanobacteria.

  • Oxygen-farting was a good thing for eukaryotes, since we rely on oxygen to power our cells.

  • We can only do that thanks to mitochondria, which, as you may have heard,

  • are the powerhouse of the cell.

  • And mitochondria's origin story is very cool.

  • Scientists think an early single-celled organism swallowed a bacterium

  • but didn't digest it.

  • And amazingly, this was the beginning of a beautiful friendship.

  • Together, these partner cells formed the first eukaryotes,

  • and the ingested bacteria eventually evolved into mitochondria.

  • Eukaryotes let that bacteria-turned-mitochondria stay

  • because of their special talent:

  • They use oxygen to make adenosine triphosphate, or ATP,

  • the molecule that stores and transfers energy throughout the cell and the body.

  • Mitochondria can draw energy from sugars via a cascade of electrons,

  • which they transfer to oxygen.

  • Oxygen is a great tool for this because it's good

  • at accepting those low-energy electrons.

  • So, when you're breathing, you're taking in oxygen

  • and using it to generate the energy that keeps you going.

  • But some eukaryotes developed ways to generate energy that don't rely on oxygen.

  • Now, that makes sense because oxygen

  • may not have reached current atmospheric levels

  • until around 450 million years ago.

  • So ancient eukaryotes needed to develop alternate ways of creating energy.

  • Today, there are still eukaryotes adapted to living in areas with low or no oxygen,

  • like the bottom of the ocean or the digestive systems of some animals.

  • These organisms mostly rely on fermentation,

  • which is a less efficient way to produce ATP

  • by breaking down sugars into CO2 and hydrogen.

  • But some have developed a way to breathe something other than oxygen.

  • Like the organisms recently discovered at the bottom of Lake Zug in Switzerland

  • that breathe nitrate, a molecule with one atom of nitrogen and three oxygens,

  • which they convert to nitrogen gas.

  • Unlike most oxygen-breathers, who breathe in O2 and breathe out CO2.

  • The waters at the bottom of this lake are oxygen-depleted but brimming with nitrate.

  • So you can see why these little Swiss survivors

  • need to make use of the ingredients in their environment.

  • They still seem pretty strange, though, because they do not have mitochondria

  • and they do not do fermentation.

  • But they are living, breathing eukaryotes.

  • They just don't breathe the same stuff we do.

  • So, how do they manage it?

  • Well, like the first eukaryotes, they aren't doing it solo.

  • They have an endosymbiont,

  • a little buddy living inside them that performs functions that keep them alive.

  • This inner partner does the same job as mitochondria,

  • only instead of transferring electrons to oxygen, it transfers electrons to nitrogen.

  • The partnership is so successful that researchers think it's been around

  • for two or three hundred million years.

  • We know of some other organisms that can breathe nitrate,

  • but it's very unusual to find one that doesn't also use O2.

  • Also, there's an intriguing difference between the endosymbiont and mitochondria.

  • When mitochondria evolved, they started as swallowed bacteria

  • that gradually ditched some of their genome

  • and integrated more closely with their host cell.

  • And then eventually they became an organelle, or little organ, of their host cell.

  • But in the Swiss eukaryotes, the endosymbiont isn't an organelle.

  • It's still a bacterium.

  • And the researchers think it may be on its way to becoming an organelle.

  • We may be witnessing an evolution

  • similar to the one that took place billions of years ago,

  • when those mitochondrial ancestors

  • first teamed up with another cell to form eukaryotes.

  • There are a lot of things we still don't know about this, though.

  • Like, this relationship could be totally unique.

  • Or maybe it's not.

  • Maybe the fact that it's similar to what we think happened with ancient mitochondria

  • suggests that this kind of relationship happened in other eukaryotes,

  • we just haven't seen it yet.

  • And if endosymbionts can help their host breathe nitrate or oxygen,

  • then what about other compounds?

  • Also, where did this relationship evolve?

  • Like, probably not in Lake Zug, which is only ten thousand years old.

  • In fact, researchers have found the Lake Zug

  • endosymbiont's genes in other parts of the world,

  • in much older lakes.

  • So, it's a prolific little thing, with an origin story that's still a gigantic mystery.

  • We do know, though, that his relationship has a lot to teach us about how life

  • can find ways of surviving in places where survival seems improbable.

  • And it might even shine some light on our own very distant origins.

  • If this video has left you wanting to learn even more

  • about life's surprising complexities,

  • then you might enjoy a course from Brilliant.

  • Computational Biology will teach you about the overlap

  • between computer science and biology,

  • which biologists use more and more.

  • Like to predict how a complex molecule will fold,

  • or compare genome sequences to one another.

  • And you're sure to find a course that suits you from their collection

  • spanning from math to computer science, and basic science to engineering.

  • All with illustrated, interactive exercises to help you along the way.

  • If you're interested, you can check out Brilliant.org/scishow

  • for a chance to get 20% off an annual Premium subscription.

  • And thanks!

  • [♪ OUTRO]

Thanks to Brilliant for supporting this episode of SciShow.

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Meet Our Nitrogen-Breathing Bacterial Relative

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    joey joey に公開 2021 年 06 月 03 日
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