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There are only a few groups of bacteria that do this kind of gliding, but they’re found across a plethora of environments, including ponds, soil, and, surprise, in our own mouths.

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SOURCES:
https://microbewiki.kenyon.edu/index.php/Beggiatoa:_Focus_on_Current_Research
https://pubmed.ncbi.nlm.nih.gov/11544349/
https://www.nature.com/articles/s41598-017-18160-w
https://microbewiki.kenyon.edu/index.php/Cyanobacteria_and_Cyanotoxins
https://ucmp.berkeley.edu/bacteria/cyanointro.html
https://pubmed.ncbi.nlm.nih.gov/10985737/
https://microbewiki.kenyon.edu/index.php/Cyanobacteria_and_Cyanotoxins
https://elifesciences.org/articles/70327
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The first hundred people to   click the link in the description  will get a free one-week trial.  When you look out at a pond, you are rarely  ever staring at just a body of water,   some sort of liquid mass separate from the trees  and vegetation around it. The pond itself is   usually full of life, sometimes as large as  a fish, sometimes as small as a bacterium.  But sometimes those tinier organisms come together  to form large colonies that coat the sediment   in and around the pond.

Like these beggiatoa,  which might look like bits of string unfurling   underneath the microscope, but are actually  hundreds of individual bacteria that have   attached to each other to create a filament. Beggiatoa are sulfur bacteria, and you can   see the sulfur they’ve all stored  shining as the filament glides past,   glittering like a diamond-studded bracelet. And just as the bacteria gather to form a   filament, the filaments gather to form a  mat, weaving together tens of thousands of   beggiatoa into a white carpet that lines surfaces  found in marine and freshwater habitats alike.  And that is great news for James, our master of  microscopes, because one of his sampling ponds   happens to have some of these beggiatoa carpets,  making it very easy for him to just collect a bit   from the mat to check out under the microscope.

Or at least, it used to be easy.   Recently, for some reason, the pond hasn’t  yielded quite as much beggiatoa as it used to.   In fact, it’s barely produced any.  We don’t know quite what happened,   but James suspects a new resident of the pond:  a family of beavers that could have potentially   changed some of the chemical composition,  making it less habitable for the beggiatoa.  But in its place, another bacteria has come  to take over the thick biofilms of the pond:   filamentous cyanobacteria. And while there’s  plenty to distinguish one from the other,   there’s one very important trait  that unites them and makes them   similarly mysterious: it is in the way they move. Maybe you’ve picked up on it already.

The long   lengths of beggiatoa and cyanobacteria gliding  across the slide. There are only a few groups of   bacteria that do this kind of gliding, but they’re  found across a plethora of environments, including   ponds, soil, and, surprise, in our own mouths. Those fast-moving bacteria are largely   moving with the aid of flagella,  a helical structure powered by ATP   that propels the bacteria in different directions.  But gliding does not involve those flagella.  Gliding involves something much more slick  than flagella: complex polysaccharides, which   scientists call by a much cooler name, slime.

A thread gliding across slime sounds more   like an arts and crafts project gone wrong  than a complex form of motion that shapes   entire ecosystems. But of course, that  is exactly what gliding turns out to be.  To appreciate the importance of this  movement, let’s continue with cyanobacteria,   which have been photosynthesizing and  oxygenating our world for billions of years.  They are small, but the impact they are  able to have on the world around them   is huge. And all this without the  aid of flagella to move them around.  Of course, it would be a massive challenge for  cyanobacteria to survive if they couldn’t move   anywhere.

They are photosynthetic organisms,  after all, so even if they’re not hunting   down prey, they are on the hunt for sunlight. Fortunately, they already have the tools in   place to sense sunlight. The pigments they use  to perform photosynthesis can also—when they   detect light— set off the reactions that drive the  cyanobacteria in the right direction.

But not all   light is the same: some species of cyanobacteria,  for example, will glide away from blue light,   while others ignore color and instead gauge  their response based on the intensity of light.  These responses will vary with the  species, as will the way they glide.   Some can bend, others can rotate around the axis  of their filament. But the end result is the same:   a slow, but directed movement in search  of light that will one day be food.  But these filamentous cyanobacteria have hit on  more than just a steady, graceful path towards the   light. They are collective organisms, gathering  into filaments and mats.

They can even aggregate   into toxic blooms that can span hundreds of square  miles, suffocating or poisoning the unfortunate   organisms that come in contact with them. And one of the challenges of forming   these kinds of collections is that it  requires diverting resources towards   making the extracellular structures that keep the  cells together. And that can come at the expense   of dividing and making more cyanobacteria.

So if there are disadvantages, there must   be an advantage, and there’s a big one. By working  together, these colonies can allow the individuals   to better pursue a collective goal. And gliding  happens to just be one of those collective goals.  In the case of the model cyanobacteria species  Synechocystis, researchers have found that while   individuals of the species can navigate in  response to light, they’re better able to   orient themselves to light when they’re attached  to each other.

It’s like they go from stumbling   individuals to a well-choreographed dance line. And the mathematical models suggest that even   if a fraction of this colony can’t respond  to light, the overall movement around them   will stay the same—taking everyone towards light  and towards photosynthesis and continued life.  So this seemingly simple movement  brings complexity to these   seemingly simple organisms. And scientists  have been trying to decipher the mechanisms   that drive gliding for many decades now.

We mentioned earlier that where there’s gliding,   there’s also slime. But we don’t know what that  slime is actually doing. There have been theories,   of course.

In one potential mechanism, the gliding  cyanobacteria oozes slime to power it along the   surface. In another, waves travel down the length  of the filament to push it along the surface.  But even as scientists have identified more  of the components driving the movement of   filamentous cyanobacteria, the process—or even  whether there is just one process—remains unclear.  It seems like it should be so much more obvious,   doesn’t it? That there should be an easy  answer.

We know so much about flagella,   and our own system of locomotion with  leg, well, that seems pretty obvious.  But then, maybe that’s what makes this so  beautiful and infuriatingly difficult to explain,   despite how long we’ve been  working to explain it. For now,   at least, it is a movement without an obvious  metaphor. one day, we’ll think of something.  Thank you for coming on this journey with us as we  glide through the unseen world that surrounds us  Thank you also to Endel for  sponsoring this episode.  Endel is an app that creates personalized  soundscapes to help you focus, relax, and sleep.  It uses AI technology, the pentatonic  scale, and pure intonation to create simple,   pleasant sounds that can help to calm your mind. Sound has a direct impact on your physical and   mental wellbeing, and by adapting in  real-time to things like your location,   your weather, your heart rate, Endel can help you  out, whether you just want to sit back and relax   or if you’re having trouble getting a good, deep  sleep.

And if you’re looking for something to   study to, you could check out their new Deeper  Focus collaboration with musician Plastikman.  If you’re interested in trying out Endel, you  should try to be one of the first 100 people to   click on the link in our description, because  if you do, you will get a one-week free trial.  There are now, arriving on your screen, a bunch  of names. These are people all across the world,   who support us on Patreon. We have a little, weird  show here, and it’s not designed to go super duper   viral and get a huge huge audience so that it can  buy lots of expensive microscope equipment.

So,   instead, we have Patrons on Patreon. They’re  lovely. They’re the reason we can make this show.   Thank you to all of you, so much.

If you want to learn how to become a patron,   you can go to 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 form us, there’s  always a subscribe button somewhere nearby.