This episode is sponsored by Magellan TV,   a documentary streaming service, founded by  filmmakers.

Journey to the Microcosmos viewers   will get a one-month free trial on Magellan TV  by clicking on the link in the description. Let’s start today by agreeing on one  thing: this is weird.

We’re looking at   a dark purplish screen with little bits of white  floating towards the top, as if they’re bubbles   rising to the top of a glass of grape soda. But that’s not the weird part.   The weird part happens when those bubbles suddenly  move in concert away from the frothy edge,   dragged towards one corner of the screen and  then towards the other. The effect is cosmic,   like we’re watching a million stars get  flung towards each corner of the sky.  And it won’t make it any less weird to know that   we’re not looking at bubbles or  stars.

We’re looking at bacteria. A field of them shaped by an invisible  force they are innately built to respond to.   Every swing towards one direction and then  another is visual proof of this unseen thing.  So what is it? What is the force  that’s driving them to move this way?  Technically, it would not be wrong to say that  the answer is James, our master of microscopes.  When James first saw these bacteria, all he knew  is that they came from a sample taken from a   Portuguese beach.

And on each slide, the bacteria  were swimming in a stark line. And usually,   it’s not that strange to find bacteria swimming  in a line, especially when you realize that those   lines fall along particular chemical gradients  that correspond with the bacteria’s own needs.  But what was weird to James is that the bacteria  seemed to be congregating entirely on one side   of the slide. Now at first, he thought that there  might be some kind of food source over there   that was drawing the bacteria towards that  edge.

So when he disposed of the slide,   he moved on, not expecting to see it happen again. But the next day, James took a drop of water   from his sample and added it to the slide. And  there it was, another line.

Just like he had  seen the day before, but the line was sticking to one  side of the slide, almost as if they were being   pulled by some invisible string in that direction. And that gave James an idea. He took out his phone   and opened up his compass app.

Then he placed  the phone on the microscope stage to see what   direction the bacteria were swimming in. And he  found that the bacteria were all swimming north.  So if we’ve seen this line of bacteria that’s all  swimming north, what’s with the other things we’ve   been watching, where the bacteria look like  they’re being dragged in other directions?  Well, as soon as James realized that his bacteria  were swimming north, he decided to go and grab   some magnets to see if he could trick them into  thinking some other direction is north instead.   So he held the north end of the magnet close to  the slide, and the bacteria began to migrate,   drawn in the direction of the magnet. And then, he rotated the magnet so   that the south end pointed closer,  driving the bacteria to swim away.  What James had found—what we are seeing  in action—are magnetotactic bacteria,   or bacteria whose movements are  controlled by the earth’s magnetic field.  Magnetotactic bacteria were first described in  1963 by an Italian scientist named Salvatore   Bellini, who found them living in freshwater.  And when he saw them move with the same singular   northward focus that ours have been exhibiting,  he considered the idea that they might have   some kind of internal compass within them.

But  while Bellini wrote up his work, it was only circulated as manuscripts to some of the universities in Italy instead of being published   in a journal for more scientists to find. That meant that the existence of these bacteria wasn’t widely   known when a decade later, a graduate student  named Richard P. Blakemore collected some more bacteria   from a pond in Massachusetts and witnessed that  northward microscopic migration for himself.   Blakemore coined the term “magnetotaxis” to  describe what they were doing.

And as he dove   deeper into the bacteria to understand how they  moved this way, he realized that they did in fact   have their own internal compass. Or rather, compass-es.   Within these bacteria are a set of organelles  called magnetosomes. The core of the magnetosome   is a magnetic crystal—either iron oxide or  iron sulfide—that’s made through a series   of processes that involve the cell taking in  iron from its surroundings and mineralizing it   within them.

The crystal is then wrapped in  a membrane to create a single magnetosome.  But as we said, magnetotactic bacteria don’t just  have one magnetosome. They have a set of them,   usually around 10 to 20, arranged in a chain to  create a dipole that can respond to the magnetic   field that crosses the world around the bacteria. Magnetotactic bacteria are found all around the   world, but their preference is to live  in areas with low levels of oxygen,   like deeper down towards the sediment and  away from the surface.

And this preference   has potentially important consequences for the  direction that magnetotactic bacteria travel in.  All of the magnetotactic bacteria discoveries  we’ve described so far, including the bacteria   that we’ve been watching, travel north. However,  all of those bacteria share something else in   common besides their propensity towards the North 

Pole: they all live in the northern hemisphere.  Meanwhile, scientists have found that magnetotactic bacteria from   the Southern Hemisphere will actually  travel towards the South Pole.  This is probably due to the incline of our  planet’s geomagnetic field lines, which   mean that as a bacterium travels towards its  specified pole in its preferred hemisphere,   it also swims downwards in the water  towards the sediment it prefers.   If a magnetotactic bacterium from the Southern  Hemisphere was forced to navigate the magnetic   field of the northern hemisphere instead,  it would find itself swimming upwards,   reaching waters higher in oxygen and  far less comfortable for the bacterium.  At least, this is the hypothesis for why this  apparent polarity within the distribution of   bacteria exists. But as always, there are  exceptions—southern-seeking bacteria found   in the northern hemisphere, and other strange  behaviors that scientists are still deciphering.  There are many other mysteries to magnetotactic  bacteria, like what advantages magnetism   even gives them—whether it’s to find the right  habitat in the water, or to hunt down particular   nutrients, or a combination of different factors. And the bacteria probably don’t know why they   move this way either. It is simply baked  into them, a crystal that draws them   into invisible tracks.

They are mysterious and  enigmatic. You might even call them, magnetic.   Thanks for coming on this journey with us as  we explore the unseen world that surrounds us.  And thank you again to Magellan TV for sponsoring  this episode of Journey to the Microcosmos.   There are a lot of unseen worlds that surround  us, and while we tend to focus on the ones we   can fit under the microscope, the James Webb Space  Telescope is out there studying the atmospheres of   exoplanets, and searching for the building blocks of  life elsewhere in the universe. And you can learn   even more about that by watching Planet Hunting  With The James Webb Space Telescope on Magellan TV.  Magellan TV is a documentary streaming  service, founded by filmmakers.  It has some of the most in-depth  Science content available anywhere:   covering space, technology, nature, and more 15 to 20 hours of new content is added   each week with a growing collection of 4K,  high-definition content for no additional cost,   so you will never run out of something  to watch, and there are no ads.  Magellan TV can be watched anytime, anywhere,  on your television, laptop, or mobile device   because it’s compatible with Roku,  AmazonFireTV, AppleTV, Google Play, and iOS  Click on the link in the description to get  your first full month of Magellan TV for free.  All the peoples names you see on the screen  right now, they are the people who support us   on Patreon.

They give us a little money, so that  we can continue making this show, because look,   we understand that we are extremely excited  about magnetotaxis, but many people aren’t, and   that’s okay. It’s a big diverse world. But with  tools like Patreon, and great people like these,   amazing content about amazing bacteria, can still  survive on YouTube.

So thanks to much to all of   them, and if you want to join them, you can go to  Patreon.com/JounreyToMicro. If you’d like to see   more from our Master of Microscopes James Weiss,  make sure to check out Jam & Germs on Instagram,   and if you’d like to see more from us, there’s  probably a Subscribe button somewhere nearby.