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It's time to meet a single-celled organism that is bigger than a tardigrade! We'll learn how Stentors reproduce, why they look like trumpets, and why some of them are just SO BLUE!

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"Corrections: 00:16 In this video we said that tardigrades have six legs, but they actually have eight legs."
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 millimeters 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 organelle 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, “stentorin” but 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 ciliates 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.

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