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Today's episode has one particular theme: a bunch of funny things going on in the microcosmos.

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A quick reminder before we get into today’s episode.

We now have a 2024 Microcosmos calendar available. It features images from 12 of our most popular Journey To The Microcosmos videos, and you get yours now at We’re going to do something we don’t usually do on this channel.

We’re going to play a clip in reverse. If you were to describe what you’re seeing, you might say something like “it looks like someone dropped a bowl of rice on the ground.” Or maybe you'd come up with something more eloquent, something that captures the array of gray and green and maybe even faint bits of purple. But as we’ll see in a bit, there’s something kind of funny going on with this group.

In fact, let’s call that the theme for today: a bunch of funny things  going on in the microcosmos. We’re going to return to this footage throughout our video today. But we’ll also be visiting some of the other  unusual finds that James,  our master of microscopes, has made recently.

And when we do return to this scene, just remember that we’re playing it in reverse. For now, let’s just take a second to describe some of what we’re seeing. The bright green cells are algae, and the purplish organisms are purple bacteria.

And it’s unusual to find these two organisms so closely associated because they usually reside in such different environments. The green algae prefer oxygen, while the purple bacteria avoid it. And yet, as we keep watching, they seem to come closer and closer together.

So as we go back in time, why are these two very different organisms finding their way nearer to each other? Well, we’ll return to that. But in the meantime, let’s take a look at this strange S-shaped organism in the middle of your screen.

Scientists have been arguing about what that organism is since 1847, when a Danish scientist named Eugenius Warming wandered along a beach and found this organism in his samples. Some have argued that it’s a single organism, a flagellate of some kind. Others have argued it’s a bundle of bacteria.

Either way, the organism was given the name Pelosigma. The screen is getting bright now because James is shining a bright UV light on the samples. And as the view recovers, you’ll see that the Pelosigma has fully devolved into a loose bundle of threads.

This matches the conclusion that scientists had come to as well, that pelosigma is a group of bacteria. In its normal form, pelosigma is an aggregate of S-shaped bacteria. But the UV light James shone on them blasted them apart.

So while we settled one mystery by watching organisms fall apart, let’s return to watching the unlikely duo of purple bacteria and green algae approach each other. Except, of course, we’re going back in time, so what we’re really doing is watching these organisms move back to the original condition that defined them to begin with. But what was that condition?

Well, it seems like they were probably in some neatly arranged pattern that intermingled their populations. But before we examine exactly what that organized arrangement is, let’s check out what looks like a much less coordinated grouping. These are three ciliates called Spathids, and they really look like three water balloons playing a very violent version of tug of war.

But they’re actually doing something kind of lovely. They’re engaged in conjugation, which is a form of sexual reproduction that ciliates can undergo to produce offspring. The thing is, conjugation usually happens between two organisms.

So you’re probably wondering why are there  three spathids involved in  this particular exchange. Are ciliate conjugation threesomes a thing? Well, we wish we could tell you, but we have no idea.

Dr. Genoveva Esteban, who James often works with, said she once saw three spirostomum conjugating. So this isn’t the only time something like this has been observed between ciliates.

But it doesn’t seem to be a well-documented behavior, so we don’t know why it happens or what’s going on with the individuals involved. James did check on the Spathid trio after they were done, and they seemed to be doing well. Which oddly brings us back to our purple and green duo.

Because as we’ll see any second now… That duo is actually a trio, though in a slightly different form. This isn’t conjugation, it’s endosymbiosis. The new member of our group is an organism  called Pseudoblepharisma  tenue, and its single-celled body is host to that crowd of green algae and purple bacteria we were watching before.

At some point, the pseudoblepharisma died,  spilling its smaller  residents into the microcosmos as we saw in the beginning of our video. While the pseudoblepharisma is sadly still dead, the magic of video means that we were able to resurrect it in a way, reversing its tragic fate if only through the power of editing. It isn’t unusual to find green algae like these living inside of other organisms.

We’ve seen relatives of this algae in ciliates like paramecium bursaria, where they provide the products of their photosynthesis to their host in exchange for protection from their surroundings. What is much less common, however, is to find purple bacteria symbionts. And what is even less common than that is to find a combination of purple bacteria and green algae endosymbionts.

In fact, this might be the only example we know of. Most of the endosymbionts are the purple bacteria, which are similar to purple sulfur bacteria except for the sulfur part. Instead they seem to have lost much of their ability to work with sulfur, perhaps because their host provides many of the nutrients they need in exchange for the metabolic talents the purple bacteria have retained.

Like we said early on, green algae like oxygen, and purple bacteria don’t. And while both perform photosynthesis, they rely on different photosynthetic pigments, which in turn absorb light  at different wavelengths. So imagining these two organisms trying to make a home out of the same host seems like watching a battle between two deeply incompatible roommates.

And yet, they seem to do just fine. In some ways, you could see where this is a good deal for the host, who now has two organisms who can produce nutrients under different conditions. But strangely, despite the flexibility that might suggest, Pseudoblepharisma tenue tends to dwell in primarily low oxygen sediments— the preferred habitat of the purple bacteria.

Scientists are still understanding how this unusual threesome works, and how the presence of these two different endosymbionts shapes the behavior of their host. We envision it as something kind of like kids yelling from the back of a minivan, shouting conflicting demands at their parents who are in turn focused on the actual schedule for the day. Perhaps it’s strange to conjure up that image in the microcosmos.

But in our defense, the microcosmos manages to craft far more unusual sights. Thank you for coming on this journey with us as we explore the unseen world that surrounds us. We’d also like to say thank each and every one of our Patrons.

Some of their names are on the screen right now, and these are the people that make this channel, and videos like this possible and we are very grateful. If you’d like to become one of them, you can go to If you’d like to see more from our Master of Microscopes, James Weiss, you can check out Jam & Germs on Instagram, and if you’d like to see more from us, there’s probably a subscribe button somewhere nearby.