Back in the 1960s, biologists thought that certain environments, like hot springs, were just too hot for bacteria to live in.

They weren’t supposed to be able to survive temperatures above 55 degrees Celsius. Proteins, one of the building blocks of life and key doers-of-things in cells, tend to break down when things get that hot.

So microbiologist Thomas Brock was surprised to see cyanobacteria living in one of Yellowstone National Park’s famous geothermal pools when he stopped there on a whim to break up a long road trip. That chance stop would lead to the discovery of a new, heat-loving bacteria, to a rethinking of the limits of life, and to a revolution in modern biology. Who said a Bizarre Beast has to be an animal?

It’s time to meet Thermus aquaticus. [ ♪ Intro ] While we usually introduce you to a member of the animal kingdom on this show, we wanted to switch things up for April Fool’s Day, why limit our exploration of weird life forms to things that can be seen without a microscope? And animals and bacteria are definitely living things, unlike viruses, which some scientists don't think are alive and others do. Now, there are two main differences between bacteria and animals: how many cells they’re made of and how those cells are set up.

Bacteria are single-celled and they’re what are called prokaryotes. Their cells don’t have a nucleus or any membrane-bound organelles. In contrast, animals are multicellular and they’re eukaryotes.

Their cells have nuclei and organelles. And our Bizarre Beast this month is the bacterium Thermus aquaticus, the most important bacterium you may never have heard of. It’s rod-shaped, which is a pretty common shape for bacteria, yellow, and sometimes makes long, stringy filaments that are visible to the naked eye when it grows in water that’s hotter than its preferred temperature.

And it doesn’t cause disease or do anything that we think of now as particularly weird or extraordinary. It just lives its best microscopic life in water that’s around 70 degrees Celcius, thriving on the energy it gets from chemical reactions, rather than sunlight. And while it was originally discovered in Mushroom Pool in Yellowstone, it has since been found in many different places, including thermal springs in California, a huge underground aquifer in Australia, and hot tap water in Indiana .

And no, I don’t know what Thermus aquaticus was doing in the tap water. The scientist that discovered it in Yellowstone just decided to see where else it might be living and sampled the tap water in his department building at Indiana University, I guess. Which kinda feels like you went on a safari to see some supposedly rare, mysterious animal, then got home and found one going through your trash can.

Anyway, we know now that Thermus aquaticus is a pretty common bacterium that can live in a lot of different environments, both natural and human-made. But when it was discovered, its ability to thrive at temperatures hotter than what microbiologists thought was possible forced them to stop and rethink what the limits of life could be. If bacteria could survive at those supposedly unlivable temperatures, what about places that seemed too cold?

Or too acidic? Or too dry? Thermus aquaticus opened the eyes of scientists to the world of so-called extremophiles: organisms that inhabit environments with very challenging conditions, places like deep sea vents, for example.

And that wouldn’t be its only contribution to science. Because, it also revolutionized modern biology in a way that’s still a big deal today. See, in the 1980s, scientists were looking for better ways to study DNA - or, more often, specific genes or sections of a genome.

And that meant they needed to be able to isolate the right bit of DNA from the whole genetic code, and have enough of it to use in experiments. The way they would do that was to snip out the gene and insert it into the genome of a bacterium, which would then replicate both itself and that bit of DNA, giving them enough material to work with. But this process was labor-intensive, there had to be a more efficient way.

Enter PCR, or polymerase chain reaction: the process that’s still used today to make many copies of a piece of DNA quickly and easily. The basic way it works is by heating up the DNA so that the two strands that make up its double helix unzip from each other. Then, each strand can be used as a template to create a new copy of the double helix, with an enzyme called a DNA polymerase doing the work of adding the building blocks needed to complete the template.

Those two new copies can then be heated, unzipped, and used as templates again, giving you four new copies of the complete double helix, and so on. But, like the original method of copying DNA, this one took a lot of work. Because, like we mentioned at the beginning of this story, enzymes are proteins and heating them up usually breaks them down.

So, for each round of DNA copying in the old school PCR process, new enzymes had to be added, meaning a scientist had to essentially babysit the whole procedure. Until one researcher suggested trying out a DNA polymerase enzyme isolated from a bacteria that thrives in hot springs. If Thermus aquaticus could copy its own DNA at those high temperatures, its enzymes must still be functional.

And it worked! Thanks to Thermus aquaticus, PCR became faster, easier, and cheaper than before. Like the discovery of the bacterium itself opened the eyes of scientists to the world of extremophiles, its DNA polymerase was the key that unlocked the world of genomics.

Since then, PCR has been used for everything from studying HIV, to the Human Genome Project, to sequencing ancient DNA from our extinct relatives, to, yes, even COVID testing. And while the mega fauna of Yellowstone may be what we think of as the iconic wildlife of that park, it’s worth remembering that some of the tiniest things living there are equally wild. In honor of April Fool’s Day 2022, we have a special, limited-edition pin that you can only order TODAY, if today is April 1st, 2022.

Check out this little hot spring! The deepest part of the pool is glittery! And it’s the perfect complement to this month’s pin club pin, Thermus aquaticus.

You can sign up for the Bizarre Beasts pin club from now through the end of April 3rd. When you sign up, you’ll get the Thermus pin in the middle of the month and the pins after that around the time each new video goes live. As always, profits from the pin club and all our merch go to support our community’s efforts to decrease maternal mortality in Sierra Leone. [ ♪ Outro ]