Thank you to Skillshare for supporting this
episode of Journey to the Microcosmos. If you are one of the first thousand people
to click the link in the description you can get a two-month free trial of Skillshare’s
Premium Membership. The word that comes to our minds when bacteria
take the stage is “chaos.” Each individual may be so small as to feel
insignificant, but the combined presence of all of those tiny shapes in so many different
states of excitement can be difficult to make sense of. In fact, in the 18th century, Carl von Linné
grouped the microbes he observed together and named them “Chaos.” The label didn’t last in part because it
wasn’t exactly specific, but the feeling endures. Even when the movement seems more ordered,
it’s baffling to watch. Like these little wiggles that seem so snake-like
except for the unsettling vibration that’s added on. Or you might see a mass of bacteria collectively
spinning in place like a very odd, microscopic flash mob. Or you could throw them all together on the
same slide and end up with what looks like several different dance parties at once. But while the movements may be a bit much
to take in when witnessed all at once, the source of that movement is almost always the
product of the same masterpiece of bacterial ingenuity: the bacterial flagella. We’ve been wanting to talk about bacterial
flagella for a while, but it’s been tough because well they’re just small and they’re
difficult to make out in our footage. Fortunately, with a lot of patience and magnification,
we have finally been able to spot them for the first time in our microcosmos journey. But we have to zoom in a bit more on this
clip, and you will need to ignore the rounder protists buzzing around. Instead, focus on the rod-shaped bacteria,
and you will see these faint lines coming off of them. Those are the flagella. More specifically, each strand you see is
a filament, which is anchored to a joint called the hook, which then connects to a motor enclosed
in the bacteria itself. Words like “hook” and “motor” imply
something made from human hands, with metal bits of machinery and fuel. But biology builds with its own materials,
and the flagella is a complex assembly made out of proteins that move like gears. And it does function very much like one of
our motors, with a stator and a rotor and gears that connect between them. But, of course, both arose independently because
if you want something to rotate, there is a best way to do it, and both nature and humans,
in this case, came up with the same solution. Though, of course for bacteria the movement
of the motor is powered by an electrochemical potential created by pumping ions across the
cell membrane instead of by an internal combustion engine. Now if you’ve been on this journey with
us for a while, you might be wondering, “Why are you talking about flagella like it’s
a new thing?” We’ve talked about tons of flagellates before,
and even explained how they move. But there is a difference here. Those flagellates are eukaryotes. And while the name is the same, the actual
appendage is definitely not. The bacterial flagella is a hollow tube that
sticks out of the cell and rotates as dictated by its motor. It actually spins around. The eukaryotic flagella is a bundle of microtubules
surrounded by cell membrane and it does not rotate, it just flips back and forth to whip
around to move the cell. And unlike the ion gradients used to power
bacterial flagella, eukaryotes rely on the energy-storing molecule ATP to fuel theirs. So, why do these two different assemblies
have the same name? Well, probably simply because when we were
originally looking at them, we didn’t know any of this. Understanding the biochemistry of these marvelous
machines has been a very long, involved, careful process involving thousands of scientists
over decades. One of the original tests to see how different
bacterial flagella were from eukaryotic flagella actually involved basically taping the bacterial
flagella down. And they found that when they did that, instead
of flopping back and forth, the bacteria themselves spun around and around. The movement of bacteria stood out to early
observers for the same reason it stands out to us: because it is so weird. There’s a mix of sporadic movements and
directed movements. But even with the significant lack of grace,
there is something coordinated underlying this movement. It comes down to what direction the bacteria’s
flagella are rotating. When the motor turns the flagella clockwise,
the filaments form a supercoil that bundles together and that drives the bacteria straight. But when the flagella is turned counter-clockwise,
the bundle comes undone, and each individual flagella moves on its own. And that creates disarray, causing the bacteria
to tumble randomly around the microcosmos. In our world, stumbling around randomly might
seem like a bit of a liability. But for bacteria, this is an evolutionarily
planned affair, helping the bacteria find food and light. Tumbling around lets the bacteria sample the
world around them, looking for chemical scents or hints of light that might point them towards
the resources they need to survive. And when they catch those signals, whether
it’s a ray of light or a chemical gradient, the flagella turn clockwise to set the bacteria
on a straight course towards their next home. So while at first glance it seems messy and
even a little broken, the bacterial flagella, it turns out, is one of the most majestic,
useful, and powerful structures in biology. Barely visible, but in our opinion, completely
deserving of a fan club all its own. Thank you for coming on this journey with
us as we explore the unseen world that surrounds us. If you’re feeling like a chaotic bacteria
tumbling randomly through your day to day life, Skillshare can help you with classes
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and design a unique, efficient planning system that works for you, in order to create a life
you love. Skillshare is an online learning community
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growth. And it makes it easy with short classes that
will fit into your daily routine. A Premium Membership will give you unlimited
access, so you can join classes and communities that are right for you. And an annual subscription to Skillshare is
less than $10 a month, and if you’re one of the first 1,000 people to click the link
in the description, you can get a 2 month free trial of Skillshare’s Premium Membership. Thank you of course and always to all of the
people whose names are on the screen right now. If you like what we do here and you’d like
to join them, you can check out patreon.com/journeytomicro If you want to see more from our master of
microscopes James Weiss, check out Jam & Germs on Instagram. And if you want to see more from us, there’s
always a subscribe button somewhere nearby.
All of my panic attacks will now somehow involve vibrating chaos snakes