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  • The most beloved of tiny organisms is probably the tardigrade.

  • Bumbly, cute, chubby, and six legged...they look like macro animals, hence their common

  • names...moss piglet and water bear.

  • And, look, we love them too.

  • We loooove them.

  • And we will talk about them on this channel a great deal.

  • But we also have a favorite species that you likely have never heard of.

  • Larger than a tardigrade, though only a single cell.

  • And the fact that you've probably never heard of Stentor is sad because they're beautiful,

  • magnificent, and powerful organisms.

  • So, Stentor...

  • It's a genus of single-celled eukaryote.

  • There are nineteen known species, but there are probably more than that.

  • Some of them can build mucus houses that they can hang out in and hide inside of.

  • Some carry algae inside of them that produce food for them.

  • And all of them are astoundingly large for a single celled organism, some can be as much

  • as four milimeters long, big enough to be seen without a microscope!

  • The biggest tardigrades, which have thousands of cells, are 1.5 mm long.

  • One thing every Stentor has in common is the holdfast organelle which lets them anchor to

  • a single location.

  • Now, they can swim, but in an undisturbed culture only a few Stentors will be swimming freely.

  • Stentors are actually more dense than water, which means that they sink, so that holdfast orgnelle

  • lets them save energy once they find a location that has plenty of food and oxygen.

  • But just because they're anchored, that doesn't mean they can't move.

  • Most stentors are also capable of stretching a huge amount.

  • When attached and feeding, a stentor body can reach to five to ten times their original length.

  • And that's when it starts to resemble a trumpet, which is where it gets one of its common names,

  • "The Trumpet Animalcule"

  • The biggest of all the Stentors, and one of the largest single-celled organisms that exists,

  • is Stentor coeruleus.

  • They can be the length of a rice grain!

  • There are insects in your back yard that are smaller than these massive, but common unicellular organisms.

  • They're in freshwater habitats all around the world, and we here at Journey to the Microcosmos

  • have a pond where we find them

  • all the time.

  • Surprisingly, they thrive even when it's freezing cold.

  • We have a Stentor culture set from Stentor coeruleus collected under 20 cms of ice.

  • Possibly, the lack of predators during the winter keeps their numbers extra high.

  • Stentor coeruleus is a part of a group called the ciliates.

  • As is true of all ciliates, Stentor coeruleus have hair-like structures called

  • cilia.

  • The beating of the cilia propels these cells in the water when they want to move around

  • and it also brings food particles, micro-animals,

  • and single-celled organisms into the cell mouth where they are taken inside the cell

  • to be digested.

  • Just like this multicellular rotifer, which is swallowed by the giant Stentor coeruleus

  • and waiting to be digested.

  • We recorded this struggle for a long time, and even witnessed the rotifer rupturing the Stentor's

  • cell membrane multiple times.

  • Each time, the Stentor repaired itself and the rotifer never managed to escape.

  • After 25 minutes the rotifer ceased its struggle.

  • Just a reminder, rotifers have a simple brain and a simple nervous system.

  • They can feel, I am not sure about pain but they can certainly feel stimuli.

  • The striking blue color makes Stentor coeruleus one of the most beautiful species of the

  • genus Stentor.

  • However, Stentor coeruleus are not just big and blue. They also have many abilities you

  • would not expect to find in a unicellular organism, including regeneration, light avoidance,

  • food selection, and reaction to mechanical stimuli!

  • Stentor coeruleus is most famous for its regenerative abilities.

  • If a Stentor coeruleus cell is cut in half, each half will regenerate into a normal looking

  • cell, at the half size of the uncut cell.

  • After healing and reconstructing the missing parts of the cell, these half-sized cells

  • will grow to the normal cell size given time and resources.

  • Even if the cell is cut into a hundred pieces, each fragment can eventually become a normal

  • looking cell.

  • Though, for successful regeneration to occur, we need two things.

  • The cut piece must contain at least part of the macronucleus and a piece of the cell membrane.

  • The macronucleus of Stentor coeruleus is visible even under low magnification, it has the

  • look of a beaded necklace, and it extends along the whole cell.

  • This macronucleus is highly polyploid, which means that even a fraction of the macronucleus

  • will contain thousands of copies of the entire genome of Stentor coeruleus.

  • Even a tiny fragment less than one-one hundredth the size of Stentor coeruleus can reconstitute itself

  • in this way if both the cell membrane and the macronucleus are present.

  • Portions of Stentor lacking either macronucleus or cell membrane only survive for a short time.

  • And the whole regeneration process takes only around 48 hours.

  • And you don't have to take our word for this.

  • Sometimes, when preparing slides, we accidentally cut these massive cells and the pieces of

  • Stentor coeruleus are left alive in the slide.

  • Within a day, they're almost fully regenerated and after two days, we can't even tell which

  • is the fragment and which are the unharmed cells.

  • Stentor coeruleus can be cannibalistic as well.

  • However, no one has ever managed to record the initial swallowing.

  • This is likely because the light of the microscope disturbs the cells.

  • Here we see a Stentor making a go of that,

  • but luckily for the little one, it's a bit too big of a bite.

  • As for that blue color, we know why, but we don't know like WHY.

  • They contain a blue pigment, “stentorinbut we don't know what purpose this beautifully

  • colored chemical serves.

  • We have guesses.

  • It's possible stentorin helps Stentor Coeruleus sense light somehow.

  • But there's also evidence that, when a predatory single-celled organism touches a Stentor Coeruleus,

  • it ejects the pigment like squid ink.

  • In some cases, scientists have observed the predatory organism pulling away.

  • Unfortunately, though we have attempted to record this process for ourselves, after many

  • hours of attempts, it still hasn't happened while recording.

  • But, remember, this isn't the only species of Stentor.

  • Here we have Stentor polymorphus.

  • This species is mostly filled with endosymbiotic algae.

  • These algae live inside of the Stentor polymorphus and produce sugar via photosynthesis and give

  • some of the extra sugar to Stentor.

  • In exchange, Stentor provides protection for the algae.

  • Look how small those algae are, if you are surrounded by thousands of different species of algae

  • eaters, hiding in one of the biggest things around would certainly protect you from getting

  • eaten.

  • Look how big they are, each dot is a Stentor polymorphus cell!

  • These cells came from an aquatic snail, it had so many Stentor cells on its shell, it

  • was visibly green!

  • Now, we've been talking about these beautiful and peculiar organisms for a long time now.

  • And there is, of course, still more to share.

  • We'll be working hard to keep our Stentor cultures alive and healthy.

  • And we haven't even talked about the peculiar way that cilliates genetic code works.

  • And how Stentor is the only Ciliate that uses the same system for encoding genes into proteins

  • that you and I do.

  • We'll have to leave that for a future video,

  • For now, enjoy these big blue beauties.

  • And hey, thanks for coming on this journey with us.

  • If you want to see more our master of microscopes, James, follow @jam_and_germs on Instagram.

  • And if you want to see more from us, that, my friends, is what the subscribe button is for!

The most beloved of tiny organisms is probably the tardigrade.

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Stentors。單細胞巨人 (Stentors: Single-Celled Giants)

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    jeremy.wang 發佈於 2021 年 01 月 14 日
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