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Hi, hello.
It’s me again, Deboki, writer and occasional host for Journey to the Microcosmos.
And I am here to confess something kind of shameful to you all: the first time I saw
a picture of a tardigrade, I didn’t think it was real.
I just remember looking at this animal that looked like a cross between a dog and the
Michelin Man.
And it was even more strange to conceive of how tiny it is, and that out there in the
world are just bits of moss with animals like this one gliding through them.
Now that I’ve spent some more time in the microcosmos, tardigrades seem almost normal.
Almost.
I mean, they are animals, and at the end of the day, you don’t have to be tiny to be
a weird-looking animal.
But animals have the advantage of many, many cells to build their different bodies.
On the other hand, unicellular organisms like bacteria and protists, have less to work with.
And yet they manage to take on so many strange and unusual forms.
Just think about it: if you were asked to draw a cell, what would you draw?
Maybe your imagination is better than mine, but I would probably sketch out a vaguely
round thing, maybe add some extra hairs on the outside if I’m feeling creative.
Nature has a lot more clever ideas though.
Trumpets and spirals and floral arrangements, all made out of single cells.
Of course, these shapes aren’t just for fun.
An organism’s shape is connected to the world it lives in, though sometimes the factors
shaping them are beyond our understanding.
It can be difficult at times to narrow down why a microbe takes on a particular shape
when the reality of the microcosmos is that in any environment, you can find a whole plethora
of shapes that might seem to have nothing in common.
It’s also easy to look at the existence of a living thing and assume that every detail
of its being has been optimized through eons of mutations and selection for a specific
purpose.
And there is an extent to which that’s true.
The world places all sorts of demands on life: the need for food, for reproduction, for warmth,
for light, for dark, for movement.
And we respond in kind by prioritizing and balancing those needs, and shape is one way
we do that.
But it’s one thing to come up with stories for why something might be advantageous, It’s
a much more involved process to prove it.
Take spirochetes, for example, which are distinctive thanks to their helical shape.
They’re also…not great for us.
They’re infectious, able to dig into us and invade our bodies.
And it’s been hypothesized that part of how they do this is through that corkscrew
shape, which might help them move through thick viscous solutions, you know, like our insides.
But proving this hypothesis took a lot of work.
Scientists spent decades studying spirochetes in viscous solutions and mouse stomachs, as
well as comparing them to other bacteria, all just to show that this shape gives them
a physical advantage in colonizing bodies.
And even then there are still so many aspects of the helical life and the advantages it
provides them that are still conjecture.
And that’s true for bacteria in general, which can take on so many shapes: spheres,
rods, filaments, stalks.
But whatever the shape, the building material is the same: peptidoglycan, a combination
of amino acid and sugar that links together to form a strong lattice that holds the bacteria
and all its contents within.
The structure of the bacterial cell wall can vary along with its shape.
One group of bacteria, called gram-negative bacteria, generally have thinner walls and
an additional outer membrane.
Gram-positive bacteria, in contrast, generally have a thicker, multi-layered wall.
But like many categorizations in biology, this dichotomy is just a tad bit too simple.
One of the largest groups of bacteria are cyanobacteria, and their diversity is even
more astounding.
There are cyanobacteria like the Merismopedia, for example, that form flat colonies held
together by a mucilaginous matrix like this, their round shape neatly arranged like candy dots.
And then you have other cyanobacteria like these long filamentous forms that glide along surfaces.
Cyanobacteria are generally categorized as gram-negative bacteria because their cells
have that extra outer membrane we talked about.
But cyanobacteria also have a thick peptidoglycan layer, which makes them sort of like gram-positive
bacteria too.
And that strange combination of traits underlies the spectacular diversity of cyanobacteria.
Single-celled eukaryotes, or protists, have a wide range of exteriors too.
But much of our understanding of their shape comes from their cytoskeleton, a network of
filaments and microtubules that coordinates many essential functions in the cell.
And when it comes to shape, it might seem unusual to focus on the amoeba, which is so
often known for its shapelessness, especially as they move.
It’s hard not to look at a blob and think of it as accidental, but the forming of pseudopodia--or
false feet--to help the amoeba move, requires a complex architecture of microtubules to
support this shifting shape.
And of course, there are many protists that take on very different shapes, whether
that’s for defense or for food or for some other reason.
There are pediastrum, that form these spiky colonies that protect them from algae eaters.
And then there are the Opercularia, which look like little flowers attached to branches,
and whose cilia you can see at work gathering food as it floats on by.
It’d be difficult to describe all the shapes that protists take on because there are just
so many, even--it feels like--when compared to bacteria.
Some scientists have argued that bacterial diversity is more internal than external,
a function of metabolic reactions we can’t see.
But protists have adapted more with their shape, leaving us with a world where the diversity
itself is multifaceted.
We’ve spent this episode talking about the diversity of shapes in the microcosmos, in
part because that’s what we can show you.
But we’ve seen over and over again the way that shapes have misled scientists when it
comes to classifying organisms, or the way that the shape of something can actually lead
to more questions that can only be answered by studying the inside of the cell.
But that’s the joy of shape: it’s an entrypoint into the microcosmos, a way for us to wonder
about organism and environment alike.
Thank you for coming on this journey with us as we explore the unseen world that surrounds us.
We’d like to also say thank you again to Skillshare for supporting this video.
On Skillshare, you can put your new knowledge of shapes to good use with classes like “Vector
Illustration: Design a Playful Character Using Geometric Shapes” which is taught by Illustrator
Jonathan Ball.
From concept and sketch to creating vectors and shading, you’ll learn how to start with
geometric shapes and ultimately end up with something from another dimension, or maybe
even the microcosmos if you decide to create your own illustrated microbe.
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