This episode is sponsored by Audible. To get started, go to audible.com/microcosmos
or text “microcosmos” to 500 500. The microcosmos surrounds and engulfs, invisible
to us until we peer through the lens of our microscope to witness the incredible diversity
of life at what seems like the smallest of scales. But there are much, much smaller scales than
this, creating a kind of sub-microcosmos. And while you may find some exceptionally
tiny life here, this is also the realm of viruses, existing in their own limbo between
what we consider living and non-living. Viruses are built of packaged genetic material,
just like any living cell. But unlike microbes and our own cells, viruses
lack the ability to replicate that genetic material. So instead, they infect, relying on their
hosts to take in their genetic material and follow their instructions to make more virus. While there are some large viruses, like the
amoeba-infecting megaviruses that can get as large as 750 nanometers, most are much,
much smaller. For context, the little crystals you see illuminated
at the tip of this closterium are about 2 microns, or 2000 nanometers long. That's almost 3 times the size of the largest
megavirus, and almost 17 times the size of most coronaviruses. So it is difficult to see viruses with the
equipment we have on hand. But this sub-microcosmos has a long reach,
extending into the microcosmos and as well into our own world. So for today, we want to talk more about some
of the ties that bind across scale. Let's start with one example of how viruses
shape life in the microcosmos. These paramecium bursaria are very, very green. They get that color thanks to hundreds of
little green algae called Chlorella that are housed in vacuoles. This relationship between the paramecium and
its internal algae is an example of endosymbiosis. And when we see examples of endosymbiosis
in the microcosmos, it's easy to focus on what the larger microbe is getting out of
the relationship. The green algae are photosynthetic, which
makes them a great internal nutrition provider to the paramecium. But symbiosis is a complicated relationship
to maintain. The Chlorella have to be housed in a special
perialgal vacuole membrane. And the paramecium can control the number
of chlorella based on how much light there is or based on when the paramecium is getting
ready to divide. So why would the algae agree to all of this? Well, protection. The microcosmos, as we’ve seen, is full
of predators both small and a little less small. But just as worrisome to the Chlorella are
the viruses, particularly the Phycodnaviridae, a group of large, DNA viruses that target
eukaryotic algae. From this group, Chlorella are particularly
susceptible to two types of viruses called NC64A and Pbi. Look, once you get down to these scales, nobody’s
thinking of creative names anymore. But when they're inside the paramecium, the
Chlorella are safe. It's like the paramecium is a kind of fence,
keeping the algae in and the viruses out. These viruses only target the chlorella when
they are released from the safe confines of the paramecium. Of course, viruses are also crafty. Scientists studying chlorella viruses found
that they were able to wait along the surface of paramecium bursaria, most likely binding
to receptors that keep them anchored to the microbe. These videos were produced by the researchers
using confocal microscopy and fluorescent stains. The big red blobs you see are actually the
Chlorella’s chloroplasts, distributed around the paramecium and making their own red autofluorescence. The green dots are produced by adding a stain
that binds to the DNA of dead cells, showing us potential locations for the virus along
the outside of the cell. If the paramecium dies for whatever reason,
the Chlorella inside of them get released. And now, not only is the Chlorella's protector
gone, its membrane is lined with the very thing the algae was trying to evade. Terrifying. The goal for viruses is to infect, to find
something that will make more of them. Sometimes they're looking to infect an algae,
sometimes they're looking to infect one of our own cells. And in a way, you can think of our skin the
same way chlorella might see a paramecium. It’s the initial line of defense against
pathogens like viruses, protecting the many cells inside us. There are other ways that viruses infect us,
but in addition to our own body's defenses, humans have created a very simple but powerful
tool for dealing with pathogens--one that we didn't even realize was so powerful until
a few centuries ago: soap. Beautiful, beautiful soap. Soap has been around for many, many millennia,
made from various oils and alkali. The goal was cleanliness: whether of objects
or of a person's own body. But it wasn't until the mid-1800s that a few
doctors began to realize that washing their hands kept their patients safer and healthier. But even as we began to understand more about
microbes and people continued to push for soap as a way to contend with pathogens, it
wasn't until the 1980s that anyone established some sort of national hand-washing guideline
for hospitals. So what is so magic about soap and washing
your hands? Well, some of it is just the movement of it
all, of water and friction scrubbing away at things that you might not even be able
to see. But part of the power of soap is simple chemistry. We can't really demonstrate the effect of
soap on viruses because, as we said earlier, we don't really have the equipment to showcase
them. So we're going to use bacteria as a proxy
instead for a simple experiment. While bacteria and viruses are different in
a number of ways, they also share one very important trait. These bacteria were obtained most professionally
from the saliva of some very cute kittens named Lupin and Sirius. That’s right, we swabbed our kitties. The membranes of these bacteria are made up
of lipids, which have a phosphate head which dissolves in water and two fatty acid chain
tails that don't. The structure of this membrane is built on
keeping these fatty acid chains away from the water that is both inside and outside
the bacteria, and that creates what's called the lipid bilayer And while viruses aren't technically living,
they can find themselves reliant on a similar chemistry. Their genetic material is enclosed in a protein
capsid. And then for many viruses, that capsid is
coated with a viral envelope that, like the bacterial membrane, is made up of a lipid
bilayer. Soap has a structure similar to these lipids,
with a fatty acid tail that wants to avoid water. And as we pipette diluted liquid soap onto
the sample, those hydrophobic tails also want to avoid water. Some do this by attempting to break into the
bacteria's lipid bilayer, ultimately breaking up the membrane entirely. Others form bubbles called micelles around
bits of bacteria and other debris. Of course, we can't see these little chemical
disruptions in action, that’s far too small a scale. What we do see is the bacterial colony quickly
melting away. Our own cells also have lipid bilayers. But we can wash our hands without them completely
dissolving away into nothing because our skin is a complex combination of protein and cells
that protects us. Instead, the soapy water destroys and carries
away the microbes that cover them, making it safer to eat and to touch and whatever
else you might be using your hands for. Viruses are tricky. They're so small and so capable of adaptation. So sometimes you have to hide out like an
algae, and other times you can rely on the basic chemistry of soap. But these are only two examples of the many,
many strategies that have evolved in nature or been developed by humans to contend with
the enormous impact that viruses can have on our lives. Nothing in this world is so small that we
cannot find a way to understand it, and nothing is so large that we cannot seek to confront
it. Thank you for coming on this journey with
us as we explore the unseen world that surrounds us. And thank you as well to Audible, for supporting
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Nobody's going to eat anything until Laura WASHES HER HANDS