This is slime. You might have expected that from the title
of the video. Even if you didn't, you might have just looked
at it and thought, "Yeah, yeah that looks like slime." Slime has had a bit of a cultural journey
in the last few decades. Some of us grew up watching green slime getting
dumped on the heads of game show contestants. And there's also been a bit of a slime renaissance
recently, with entire YouTube channels and Instagram accounts dedicated to teaching people
how to make their own gooey, sticky blobs at home with chemistry and a few simple ingredients. Of course, the most important step in any
of these slime projects is saying, "It's aliiiiiiiive," while you watch it spread, even when you know
that, of course, it’s not actually alive. The microcosmos, on the other hand, got to
its experiments long before we did, giving us slime molds: a slime that not only lives, it learns. a slime that fuses microbes together to create
a living thing that grows into something we can observe with our own eyes. You may have seen slime molds before, their
bodies sometimes laden with spores as they grow on plants and decaying wood. They look kind of like fungi, and for that
reason, that is how they were initially classified. Except that one of the defining characteristics
of fungi is their inability to absorb and digest their food internally. Slime molds, however, are plenty capable of
that. They do phagocytosis all the time. Where we see decaying matter, slime molds
detect a cornucopia of microbes. Plus, fungi do not move, and slime molds--in
their own unsettling way, do. We know now that slime molds are eukaryotes,
and they’re made up of amoeboid organisms. But they don’t fit neatly into any of our
definitions of plant, animal, or fungus, leaving them in the more ambiguous Protista kingdom
and clustered under the label Mycetozoa. However, that label is a, get this, polyphyletic
grouping, and that means that the organisms we’ve lumped together as slime molds aren’t
necessarily all related. They’ve just found their way, over the course
of evolution, into a set of similarities that is both convenient and misleading in our attempts
to categorize the natural world. There are three major types of slime molds. There are the Protostelids, which are the
least studied. Then there are the Dictyostelids, also known
as cellular slime molds, and then there’s the Myxomycetes, also known as the "true"
or "plasmodial" slime molds. Scientists love studying slime molds, particularly
Dictyostelids and Myxomycetes, for reasons that we will discuss soon. In fact, the slime molds we're going to show
you today come from a lab, though we are on the hunt to see if we can gather any of our
own in our sampling trips. This species is Physarum polycephalum, a well-studied example of Myxomycetes, making it a plasmodial slime mold. We feed it oatmeal and barley flakes, keeping
it in the dark because it's not particularly fond of light. We're observing our Physarum here on petri
dishes because it's hard to transfer them to glass slides. This, in turn, limits our magnification, so
we won’t be able to see as deeply into their bodies as we might be able to with other organisms. But they are remarkable to observe as an entity,
with their sprawling, networked branches. Now, we also don't have samples of the other
types of slime molds right now, so we're going to be focusing our discussion mostly on Physarum
and plasmodial slime molds. But both cellular and plasmodial slime molds
come up often in the news because scientists have observed them doing very impressive things,
but let’s start out by quickly explaining the differences here. Cellular slime molds, the dictyostelids, are
made up of organisms that will likely spend most of their lives as singular amoebas. But if the conditions around them become bleak,
these amoebas team up to create a multicellular thing called a "slug" that coordinates the
various cells so that they can all move to a good spot and then morph into a fruiting
body that releases spores. This is wild, right? They’re single cells and then they get some
signal that they should all come together to form an organism and spore out to create
the next generation. But while cellular slime molds are made up
of many cells, true slime molds like Physarum polycephalum are actually made up of only
one cell. Yeah, all of that branching weirdness, that
is all one cell. The life of this Physarum started with the
sporangia, a black globular body made by another Physarum. The sporangia holds spores that spread and
eventually germinate into either an amoeba or a flagellate. At this unicellular stage in their lives,
as you might expect, the Physarum only has one nucleus. But then the amoeba finds another amoeba to
mate with. And if you've heard about a slime mold that
has several hundred sexes, this is where that comes in. Each of the little cells produced by the spores
has two copies of three sex genes, and each of those sex genes has their own variants
across the species. Taking into account the number of different
combinations of those sex gene variants that are possible, you end up with an organism
whose sex is just one of hundreds, which increases the number of possible mating partners for
any individual physarum amoeba. When they do find their mate, the two become
one, literally. They fuse together all the way down to their
nucleus. And after this point, the new organism doesn’t
divide anymore. It grows. The plasmodium formed by the merged Physarum
cells expands, sometimes up to two feet in diameter if the conditions are really good. But, the nuclei inside will continue dividing
and dividing and dividing, their count ending up in the millions. Physarum have actin and myosin, or muscle
proteins, the same ones we have, that act as a part of a network to contract and relax
the cytoplasm, creating that stream you see moving through the body of the organism. This process moves the slime mold, which can
reach a speed of around 4 centimeters/hour, and it also helps distribute nutrients around that ever-widening, increasingly gigantic body. And here's the thing: whatever it is these
amoebas have come together to create, it is very, very smart. Listing off the physarum talents that have
been unearthed by scientists is enough to inspire a sense of inadequacy. They can learn to manage uncomfortable stimuli
and pass on their knowledge to other Physarums by fusing with them. They can also solve mazes and make good nutritional
choices, which, like, I can’t. In one of the most well-known Physarum experiments, scientists placed oat flakes down on an agar plate. These flakes were distributed in a pattern
similar to the arrangement of cities around Tokyo. And then they watched as a Physarum that started
at the central Tokyo equivalent eventually morphed itself into a route that resembled,
shockingly closely, the Tokyo rail system. The Physarum’s optimized hunt for food resembled
the efficiency that human engineers seek when transporting people around cities. If you grew up watching Saturday morning cartoons
or even their blockbuster adaptations, you've seen plenty of robots that assemble together
into some kind of megarobot. The bodies are metal and they’re full of
circuits, transforming the individual, fantastical powers of those robots into a bigger stomping,
punching thing. Nature, as it inevitably seems to, got there
first, beating even our imaginations, and with a touch that is so much lighter than
ours, yet still so incredible. Instead of imagined mechanical frames, it's
the organic bodies of amoeba assembling together to create a bigger living, learning thing. The contours are smooth, the movements streaming. The slime mold doesn't need to stomp or punch,
it just spreads and consumes and fruits, expanding the microcosmos in its own body as it stakes
a claim in our world. Thank you for coming on this journey with
us as we explore the unseen world that surrounds us. Thank you to all of our new viewers who are
with us and thank you especially to all of our patrons on Patreon, who make this show
possible. If you’ve just stumbled across Journey to
the Microcosmos, these people on the screen right here are the ones you really have to
thank. If you want to see more from our Master of
Microscopes, James Weiss, you can find him at Jam & Germs on Instagram, and if you want
to see more from us, you can go to youtube.com/microcosmos where we have a new episode up every week.
I like Hank's voice here in all its cool science seriousness as apposed to the usual Crash Course antics.
Thank you that was really interesting 😊 sounded like a slime mold meditation video.
So amazing.