Stentors: Single-Celled Giants – Transcript

00:08The most beloved of tiny organisms is probablythe tardigrade. Bumbly, cute, chubby, and six legged...theylook like macro animals, hence their common names...moss piglet and water bear.

00:24And, look, we love them too. We loooove them. And we will talk about them on this channela great deal. But we also have a favorite species that youlikely have never heard of. Larger than a tardigrade, though only a singlecell.

00:41And 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.

01:02There are nineteen known species, but there are probably more than that. Some of them can build mucus houses that theycan hang out in and hide inside of. Some carry algae inside of them that producefood 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 beseen without a microscope!

01:27The biggest tardigrades, which have thousandsof 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.

01:46Now, they can swim, but in an undisturbedculture 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 locationthat has plenty of food and oxygen.

02:06But just because they’re anchored, that doesn’t mean they can’t move. Most stentors are also capable of stretchinga huge amount. When attached and feeding, a stentor body can reach to five to ten times their original length.

02:22And 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 ofthe largest single-celled organisms that exists, is Stentor coeruleus.

02:40They 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 aroundthe world, and we here at Journey to the Microcosmos have a pond where we find them all the time.

02:59Surprisingly, they thrive even when it's freezing cold. We have a Stentor culture set from Stentorcoeruleus collected under 20 cms of ice. Possibly, the lack of predators during thewinter keeps their numbers extra high.

03:14Stentor coeruleus is a part of a group calledthe ciliates. As is true of all ciliates, Stentorcoeruleus 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 cellmouth where they are taken inside the cell to be digested.

03:38Just like this multicellular rotifer, whichis 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.

03:56Each time, the Stentor repaired itself andthe rotifer never managed to escape. After 25 minutes the rotifer ceased its struggle. Just a reminder, rotifers have a simplebrain and a simple nervous system.

04:12They can feel, I am not sure about painbut they can certainly feel stimuli. The striking blue color makes Stentorcoeruleus one of the most beautiful species of the genus Stentor.

04:29However, Stentor coeruleus are not just bigand blue. They also have many abilities you would not expect to find in a unicellularorganism, including regeneration, light avoidance, food selection, and reaction to mechanical stimuli!

04:47Stentor coeruleus is most famous for its regenerativeabilities. 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 missingparts of the cell, these half-sized cells will grow to the normal cell size given timeand resources.

05:11Even 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 ofthe macronucleus and a piece of the cell membrane.

05:30The macronucleus of Stentor coeruleus is visibleeven under low magnification, it has the look of a beaded necklace, and it extendsalong the whole cell. This macronucleus is highly polyploid, whichmeans that even a fraction of the macronucleus will contain thousands of copies of the entiregenome of Stentor coeruleus.

05:53Even a tiny fragment less than one-one hundredth the size of Stentor coeruleus can reconstitute itself in this way if both the cell membrane andthe macronucleus are present. Portions of Stentor lacking either macronucleusor cell membrane only survive for a short time.

06:10And the whole regeneration process takes only around48 hours. And you don’t have to take our word for this. Sometimes, when preparing slides, we accidentallycut these massive cells and the pieces of Stentor coeruleus are left alive in the slide.

06:26Within a day, they’re almost fully regeneratedand after two days, we can’t even tell which is the fragment and which are the unharmedcells. Stentor coeruleus can be cannibalistic aswell. However, no one has ever managed to recordthe initial swallowing.

06:44This is likely because the light of the microscopedisturbs 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 wedon’t know like WHY.

07:04They 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 Coeruleussense light somehow. But there’s also evidence that, when a predatorysingle-celled organism touches a Stentor Coeruleus, it ejects the pigment like squid ink.

07:25In some cases, scientists have observed thepredatory organism pulling away. Unfortunately, though we have attempted torecord this process for ourselves, after many hours of attempts, it still hasn’t happenedwhile recording. But, remember, this isn’t the only speciesof Stentor.

07:46Here we have Stentor polymorphus. This species is mostly filled with endosymbioticalgae. These algae live inside of the Stentor polymorphusand produce sugar via photosynthesis and give some of the extra sugar to Stentor.

08:02In exchange, Stentor provides protection forthe algae. Look how small those algae are, if you are surroundedby thousands of different species of algae eaters, hiding in one of the biggest thingsaround would certainly protect you from getting eaten.

08:19Look how big they are, each dot is a Stentorpolymorphus cell! These cells came from an aquatic snail, ithad 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.

08:37And there is, of course, still more to share. We’ll be working hard to keep our Stentorcultures alive and healthy. And we haven’t even talked about the peculiarway that cilliates genetic code works. And how Stentor is the only Ciliate that usesthe same system for encoding genes into proteins that you and I do.

08:55We’ll have to leave that for a future video, For now, enjoy these big blue beauties. And hey, thanks for coming on this journeywith us.

09:21If 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!