Death in the Microcosmos
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Death in the Microcosmos


This round little unicellular creature came
to us via a plankton net, a mesh with tiny, microscopic holes through which we ran hundreds
and hundreds of liters of water, letting us collect anything too large to pass through. We haven’t been able to identify this species
yet, making it a bit of a mystery. But the bigger mystery is still to come because
this little creature is about to undergo that most universal and unknowable experience of
all—death. Death comes to the microcosmos in many forms. Like this Stentor Polymorphous, slowly expelling
the contents of its once trumpet-like body into the surrounding environment. Or this dead larva, whose exoskeleton is now
an inanimate host to two unicellular organisms. Even the mighty tardigrade, which has survived
as a species through multiple mass extinctions, is not immune to death. This is, of course, the natural order of things. Predators hunt, and their prey attempts to
survive…with varying levels of success. This is Loxophyllum meleagris, a large unicellular
organism that we’ve shown before eating a rotifer. This one is practically stuffed with those
multicellular creatures. We counted five rotifers inside of it. But sometimes the predator becomes the prey,
and even the Loxophyllum meleagris has to find ways to ensure survival when other species
come after it. This seemingly unlikely threat is the Lacrymaria
olor. Its name, in Latin means “tears of a swan”,
a name that suits both its teardrop shape and its neck-like extension, which gets up
to 8 times longer than its body in search of prey. Sometimes, we can see its neck poking out
of the dirt on our microscope slide. But even knowing that, you’d be forgiven
for thinking that it’s unlikely that something so small could pose a problem for those larger
Loxophyllum. And yet, the Lacrymaria manages to take quite
a chunk out of the Loxophyllum. The Loxophyllum though survives thanks to
its ability to regenerate the piece that was taken, but not all prey gets so lucky. Here, this rotifer has been killed by a heliozoan,
destined to become food, a fate that this flagellate is about to share as it becomes
captured by a heliozoan that is in the middle of cell division. The flagellate has been trapped by those long
extensions, called axopods, that radiate out from the heliozoan’s body. As the flagellate comes further in, it will
be engulfed by the cells into its own food compartment called a vacuole. There, it will be lysed open and its contents
digested by the heliozoa. In the end though, the natural order comes
for predators too. Here, another heliozoan’s dying cellular
body attracts the various decomposers of the microbial world. Aside from predators, there are many other
factors that lead a single-celled organism to die. Changes in temperature, oxygen concentration,
pH, water quality, so much more. This single-celled organism is swollen because
the water surrounding it is entering the cell via osmosis. Many organisms have water pumps called contractile
vacuoles that they use to push water back out and prevent that swelling. But as in the case of this organism, sometimes
those contractile vacuoles stop working, and when that happens the cell swells and explodes. Other times, the cause of death is harder
to determine, like this Paradileptus that spent several hours swimming before going
still, its shape beginning to change until it melts away, seeming to kill not only the
Paradileptus but this small green cell swimming nearby…but leaving other smaller flagellates
seemingly unaffected. And this brings us back to the beginning,
with our mystery organism that is about to undergo a death laden with even more mysteries. At first, the cell looks like it’s just
melting away, dissolving into something that resembles a microbial Milky Way…except that
for a few seconds, it almost looks like the cell membrane is able to close itself back
up. We think, though we can’t know for sure,
that some of the mechanisms inside the cell are still working, and that the organism is
trying to recover. But alas, survival is not in the cards. Its membrane goes through lysis, releasing
its insides to the surrounding environment. This death is unlike any other kind of death
we have observed under our microscope, and we’re still not sure what caused it. Perhaps there were so many organisms in the
sample that they depleted the oxygen, and the organism could not continue cellular respiration,
but perhaps it was something else. Death at every size holds its own mysteries,
but it also reveals. The observations we make, even the guesses
we come up with, tell us about the way these microbes interact with their environment,
the way their bodies work, and the connections that exist between them. It is only ever in the mysteries that knowledge
is waiting to be found. Thank you for coming on this journey with
us as we explore the unseen world that surrounds us. If you want to see more from our Master of
Microscopes, James, check out Jam and Germs on Instagram where he is constantly posting
cool stuff. And if you want to see more from Journey to the Microcosmos here on YouTube there’s always a subscribe button somewhere nearby.

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