Thanks to Brilliant for supporting this episode of Journey to the Microcosmos.
Go to Brilliant.org/microcosmos check out their
Scientific Thinking course and get 20% off an annual premium subscription.
You’ve heard some worm horror stories, right? We were looking some up just for this episode and
came across a recent headline from ArsTechnica that read,
“Army of worm larvae hatch from man’s bum, visibly slither under his skin,”.
And if that’s not enough to terrify you, and make you feel very uncomfortable
there’s always the stories of painful stomach cramps or diarrhea or nausea that eventually
turns out to be caused by some worms that have taken up residence in someone’s intestines.
It is terrifying and wild to think of something so much smaller than us causing so much havoc.
So, as we watch the cilia lining a worm’s gut beat its own soothing pattern, wouldn’t it feel like,
almost like, a little bit of justice if this sight wasn’t so peaceful? If worms had to worry about
their own guts being taken over by a parasite? If you’ve found yourself in this position,
seeking schadenfreude over a worm, well we have some good news for you. The worm you see
in the middle of this tank is currently hosting this strange fellow, called a Radiophyra.
James, our master of microscopes, had been on the hunt for the Radiophyra after seeing this:
two radiophyras linked together in a chain as one divided to make more copies of itself.
It had come from the inside of one of the worms he’d been watching, when he’d
accidentally squeezed a worm a bit too hard under the coverslip and caused the ciliate to pop out.
Radiophyra belong to a general group of ciliates called Astomes,
or astomatid ciliates. We’ve talked about ciliates a lot on our channel, which means that if you’ve
been watching us for a while, you may have picked up on the fact that from time to time,
we have said that most ciliates have an oral groove, that opening lined with cilia that sweep bacteria
and algae and other tiny bits of food into the organism. We’ve seen that oral groove at work
in ciliates like stentors and paramecium, functioning as the ciliate equivalent of a mouth.
But as we have always said most ciliates, you will have inferred, that this does not mean all ciliates.
And if you are looking for an exception to the rule,
astomes are that exception. Astomatid ciliates are diverse, but they are unified by
one shared feature, or rather, they are unified by their lack of one shared feature, a mouth.
And they don’t need a mouth because they have something even better. They have worms.
Astomatid ciliates do parasitize animals other than worms. Some live inside mollusks,
others inside leeches or even in amphibians. But they are most commonly associated with the guts of
annelid worms. So when James found his Radiophyra, he decided to see if he could find more of them
in the other worms that were in his samples. And that meant that our master of microscopes had to
become a master of worm surgery, dissecting them so he could draw out the ciliates living within.
In–side this particular aquatic worm were these astomatid ciliates. From a distance,
they also look like worms. But as you get closer…
And closer, their shape becomes more definite except for the massive amounts of fluff around
them, a dense cloud of cilia beating away. Unfortunately, there isn’t a lot of research
on this ciliate. In fact, there isn’t a lot of research on astomatid ciliates in general.
They just aren’t destructive enough or common enough to have become either a necessary or
convenient research subject. In fact, it’s not even clear whether or not we should call
them parasites. Modern day papers will sometimes refer to them endosymbionts instead, because we
don't know a lot about whether astomatid ciliates are doing much to their worm hosts, bad or good.
But the worm gut does plenty for the astomatid ciliates. At one point in time,
the ancestors of these ciliates did have mouths. But as they found their way into worms,
and specifically their guts, those oral grooves became less and less necessary.
Instead, the ciliates could rely on a form of feeding called osmotrophy, where they simply
absorb nutrients from their surroundings through osmosis. Instead of taking in larger bits of
food through their mouths and breaking it down themselves, astomatid ciliates could just take
advantage of the worm’s digestive system to do all that breaking down for them. As the worm’s
digestive enzymes break down complex molecules into simpler forms that can travel through their own intestinal walls,
some of those nutrients would just go feed the astomatid ciliate instead.
These ciliates will actually sometimes be picky about making sure they’re in a particular spot
within their host’s intestinal tract. And once they’ve found the right spot,
the ciliates hold themselves in place with organelles that range in shape, some use hooks,
other spines, or maybe even suckers. The flat shape of the ciliates helps them stay pressed to
the epithelium of the intestines. So while these ciliates may not need a mouth anymore, they have
found other traits necessary to their survival. Astomatid ciliates are found in hosts from all
sorts of environments. Some live in soil. Some live in ponds. Some even live in ocean
waters. And scientists are using the general tools available now to try and piece together how host
and endosymbiont have shaped each other. We can see some of that intertwined story
in the ciliate’s mouthless-ness, but the specifics of that evolutionary change
are laid out in their DNA, as are the other more hidden parts of that shared history.
Now we cannot know whether worms have any feelings about their guts being home
to another organism. They likely don’t have much choice in the matter, and they also likely aren’t
prone to emotions like resentment the way we might resent a worm parasitizing our bodies.
But if they were to have any feelings on the matter, we want to offer this one last
detail about astomatid ciliates: many of them have their own endosymbionts as well,
bacteria that live inside them with perhaps their own history tangled up with their ciliate host’s
story as well. Now we couldn’t find those bacteria in our parasitic friends,
but we like the idea that somewhere out there are these nesting dolls of endosymbiosis: an organism
that is an organism but an organism that is also a home buried within other homes.
Thank you for coming on this journey with us as we explore the unseen world that surrounds us.
And thank you to Brilliant for sponsoring this episode.
Brilliant features hands-on, interactive courses in science,
engineering, computer science and math. And Brilliant has recently upped the interactivity
in their courses. In their Scientific Thinking course, you’ll dive into the world of scientific
principles by exploring the laws of physics and principles of engineering. Along the way you’ll
gain the understanding and insight needed to start looking at the world in a different way.
The courses are designed for people of all levels, so you can jump in
at any point and work your way to mastery. And Brilliant courses are also available offline
using their iOS and Android app. So if you’re traveling or have a spotty internet connection,
you’ll be able to keep learning. If you’re interested in learning more,
you can get 20% off an annual premium subscription at Brilliant.org/microcosmos.
The folks on the screen right now, They are our Patreon patrons.
This world of ours just doesn't stop being interesting, there is always something else
ready to blow my mind, I'm so glad that we can continue on our journey to find and share
those things, and the people here, they are the reason we can do that, so thank you all so much,
to all of you and if you are interested in joining them you can check out Patreon.com/JourneyToMicro.
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 is always a subscribe button somewhere nearby.