One week from today, we are releasing the newest shirt in our Artist Series over at
microcosmos.store.
Previously, we’ve made shirts that you can wear to show your love for tardigrades and
hydra, and now it is time to show our appreciation for the algae that produces almost half of
the air that we breathe.
That’s right, our little golden friend the diatom is getting its own shirt, designed
by Josh Quick, and it will be available for pre-order next Monday, February 6th at microcosmos.store!
Science is built on questions.
So let’s start today with a question: what do you think happens when you set off an electrical
spark in the microcosmos…
maybe something like this little fireworks show that James, our master of microscopes,
set off with a short circuit?
Perhaps your mind immediately jumps to something destructive, you've got painful
shocks that tear things apart.
That fits some of what's happening here.
The spark James created was strong enough to chip the glass slide.
It was also strong enough to break the bonds between hydrogen and oxygen in the water,
a process called electrolysis.
We can’t see those individual atoms separating from each other, but we can see the end result:
hydrogen and oxygen bubbles that build and burst in front of our eyes.
Or maybe you think that electricity is more of a productive force,
something that creates instead of breaks.
And that too fits some of what we see here.
That same electricity that broke apart water molecules also created a world of charged
particles, painting an otherworldly landscape in the process.
You may also be a fan of a third option: chaos.
Your mind replays images of frog legs zapping to life or hair defying gravity as electricity
flows through limbs.
The answer, honestly, might—ahem—shock you.
It was certainly not what I would have expected.
So what happens when you apply an electric field to the microcosmos?
Order.
Watch as this whirlwind of ciliate activity un-whirlwinds itself, abruptly shifting to
a uniform direction of movement as if someone whipped out a bullhorn and yelled at them
to get in line.
Of course, there is no invisible person with a bullhorn.
There is just James, and a power supply that he used to create an electric field across
the slide.
The movement that the ciliates are showing is a particular form of motion called “galvanotaxis,”
though you might also hear it called “electrotaxis.”
Many organisms exhibit galvanotaxis of some kind—even our own cells are capable of it.
But today, we’re focusing on a favorite group of organisms.
Our fuzzy, single-celled eukaryotic friends: the ciliates.
(Though we caveat that not all ciliates behave this way).
Galvanotaxis has been particularly well-studied in paramecium, and the ciliates we’re watching
today behave in a similar way.
But ciliates are vast and diverse.
And we’ve watched ciliates of all sorts change their motion in response to different
types of stimuli.
We’ve seen them direct themselves in the direction of chemical gradients, a form of
motion called chemotaxis.
We’ve also watched as some species either seek out light like moths, or shun it like vampires.
Those ciliates are showing a form of light-directed motion called phototaxis.
Galvanotaxis is sort of like these forms of motion in that the cells are reacting to something
in the environment around them.
For chemotaxis and phototaxis, those “something’s” are chemicals and light.
For galvanotaxis, it’s a shift in the electric potential that changes the flow of ions and
particles both around and within the organisms.
But for ciliates, galvanotaxis is also fundamentally different from those two other forms of motion.
Chemotaxis and phototaxis are both behaviors that give ciliates some kind of benefit in the end.
It can steer them towards food or light for photosynthesis, or away from threats like
predators and UV damage.
Galvanotaxis doesn’t steer ciliates to any obvious purpose or advantage.
It is just something that happens, a function of the way that ciliates themselves are built,
not something that was selected for by evolution through natural selection.
There is a whole sequence of events based on electrochemistry that drive how this happens.
It starts with an electric field, which creates a voltage gradient across the microcosmos.
This gradient interacts with the body of the ciliates, creating differences between the
interior and the exterior of the cell that cause calcium and potassium ions to flow across
the membrane.
That is the part scientists understand.
The part that happens next is a bit more mysterious.
That flow of ions changes the movement of the ciliate’s cilia—those hair-like structures
that whip back and forth to propel the organism around the microcosmos.
At the front end of the cell, the flow of ions causes the cilia to beat more frequently,
a movement called ciliary augmentation.
Meanwhile, at the other end, the flow of ions causes the cilia to beat more frequently as
well, but in the opposite direction, which is called ciliary reversal.
For the ciliate, the opposing motions of its cilia creates a torque that ultimately directs
the organism towards the cathode.
The result, as we see over and over again in our samples, is order.
The changes in ciliary motion that drive this behavior is called the Ludloff phenomenon,
named for the 19th century scientist Karl Ludloff who described its occurrence in paramecium.
At the time, he thought the movement was simply a result of electromagnetic interactions with
the cilia, but research since then has revealed the underlying physiology of the cell itself
that makes this happen.
And as we’ve said, this is—as far as we can tell—simply a function of how these
ciliates are built, a consequence of electrochemistry and electrophysiology that combines into something
that happens, with no purpose or advantage.
In fact, for some ciliates, this leads to a tragic end as they get too close to the
electrodes that inadvertently controlled them.
But that does not mean galvanotaxis is function-less.
For James, a careful application of electricity to his samples has become a valuable tool,
helping him dig up microbes that are hidden in his mud samples.
And our own bodies even are testament to the fact
that galvanotaxis can be an incredibly powerful instructor.
It directs the development of embryos, repairs our wounds, and helps grow our nerve cells.
It’s just one of countless other things that binds our lives to the history of the
microcosmos and to the invisible forces that cross all around this earth, things we humans have
found only by asking questions of the universe and chasing down the many possible answers
until we find the next question.
Thank you joining us as we explore the unseen world that surrounds us.
All of the names on the screen right now, they are our patrons on Patreon.
They are people who decide, “Heck, I want this thing to exist.
I think that it’s good.
I think that it’s lovely.
It makes me happy, brings me joy, and also, it does those things for a lot of other people.
It brings joy and knowledge to the world and I think it should exist.”
Cause it can’t exist without the support of those people on the screen right now.
And if you’re interested in becoming one of them, you can go to Patreon.com/JournytoMicro.
If you want to see more from our master of microscopes, James Weiss, you can check out
Jam & Germs on Instagram.
And if you want to see more from us, there is very likely a subscribe button somewhere nearby.