We’re going to let you in on a little secret.

One that’s maybe not actually that much of a secret: sometimes, we don’t know what we’re looking at. We’ll find a microbe that looks familiar, but the name of it eludes us.

Fortunately, we don’t need to know the name of something to show it off. So when these situations arrive, we’ll go with a name that is as specific as we can get, like the ciliate here that we refer to so specifically as…”ciliate.” But with our new differential interference contrast microscope, we’ve been able to make out all sorts of new details that we couldn’t see before. And in some cases, those new details have helped us identify organisms that we could not name before.

Like if you look closer here, you might be able to make out this little bit of a crystalline organelle. That little tiny thing is called the organelle of Lieberkühn, though it’s also known as the watch-glass organelle because it resembles a watch glass. What does it do?

We’re not completely sure, though it might be something related to phototaxis, which is how you move toward or away from light. But what it helps us do is identify what we’re looking at and give this ciliate the more specific name of Ophyroglena. Ophyroglena is a genus of histophagous ciliates, meaning that they feed on tissue.

The one we’re watching here has been drawn to this crustacean like a shark smelling a drop of blood in water, except it’s a microbe drawn to a crack in its shell. And once it gets inside, the ophryglena gorges on the tissue inside. So the Ophyroglena seems like it should be easy enough to find.

We just need to keep an eye out for the watch-glass organelle and other dead organisms. But one of the reasons it’s hard to identify these organisms is because they do not always look like this. Some ciliates have life cycles that take them through different shapes, and sizes, and activities, and responses.

It may be the same organism, but the way that it looks or behaves changes. Ophyroglena’s life cycle is made up of 5 established stages, as well as a few additional, though more rare, possibilities. The organism starts in its theront stage, taking on an elongated shape as it swims freely about the microcosmos.

It’s moving a bit quickly, so it might not be very apparent, but at this point the watch-glass organelle should be visible. The theront stage doesn’t have food vacuoles yet, but it still seeks food. It’ll swim around for about two days chasing chemical stimuli and light that point it in the general direction of food.

But once they settle down into a more restful state, they begin to fill up with food vacuoles and move on to their next stage. The Ophyroglena becomes more opaque as it transitions into its equivalent of adulthood: the trophont stage. At this point, the swimming trophont will still be drawn to light, perhaps to help hunt down the same dead tissue these bacteria are attracted to.

But as trophont gives way to protomont, the Ophyroglena starts to change as well. Some will still be attracted to light, but others will be more drawn to an absence of it. This one got stuck between some glass, but with a little water added to the slide, it’s back to moving.

Then after a few hours of eating, the protomont will begin to slow down. This is the protomont’s time for change, and so it morphs into a tomont. As a tomont, the Ophyroglena avoids the light as it prepares to reproduce.

Some Ophyroglena species form a division cyst, while others create and stay attached to a sticky substance instead. Whatever the venue, the result is the same: the tomont divides several times to produce anywhere from 4 to 8 smaller and rounder tomites whose watch-glass organelle has now disappeared. The tomites might form a chain that slowly rotates for a few hours until it separates into theronts, bringing the cycle full circle.

At times, researchers have observed deviations from this typical cycle. In some cases, the tomont might enter what’s been termed the “migratory stage,” which is noted for the largeness of the microbe and agitated movement before dividing into tomites or, in rarer cases, forming a cyst. It’s not clear what conditions would cause the Ophyroglena to enter this stage, just that it’s a thing that happens sometimes.

Now, you might be thinking to yourself, “Boy, we seem to understand all this really well.” And honestly, the many lives of the Ophyroglena would be its own business and we would probably not know all of these things if it weren’t for the fish problem. In 1959, scientists at the Eastern Fish Disease Laboratory at the U. S.

Bureau of Sport Fisheries and Wildlife reported that several of the fish in their aquarium had died soon after being infected with a ciliate. The epithelium of the infected fish had sloughed off and been marked with white spots. With the right lighting and background, the researchers could even see a mass of ciliates swarming around the fish.

In their descriptions of the ciliate, you can see the hallmarks of the Ophyroglena life cycle. When active and feeding, the culprit had an elongated shape. And after dining on their course of fish, they would become more rounded and descend to the bottom of the aquarium.

This fish-feeding frenzy does not seem to be typical of Ophyroglena. At the very least, this report is the only one we’ve found of its kind, though they do have a documented history of infecting insects. But in the case of the fish infection, the researchers compared Ophyroglena to the obligate parasite Ichthyophthirius multifiliis, better known as Ich or just Ich disease in fish.

The symptoms of both of these infections are similar. And Ichthyopththirius is a ciliate whose life cycle has many steps in common with Ophyroglena, including tomites. The life cycle of Ich disease is formatted around the fish the parasite must infect to survive.

And as such, the ways of fighting it are also oriented around interfering with this process of change and growth in the microbe itself. Ophyroglena may not have the same infectious mandate, but the parallels between their lives and that of other disease-causing ciliates shows why understanding life cycles isn’t just about how an organism changes over the course of its own lifetime. It’s also about how those changes in turn affect the world around them, as we all, even the small of us undoubtedly do.

Thank you for coming on this journey with us as we explore the unseen world that surrounds us. And thank you, as always, to these people on the screen right now. If you like this show, these are the folks you should thank.

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