Thermus aquaticus

by Veronique Greenwood

When microbiologist Thomas Brock fished some pink threads out of a Yellowstone hot spring in 1969, it was common knowledge that bacteria couldn’t thrive above 131 oF. But, as Brock soon found, common knowledge was wrong. There were organisms in that pinkish gunk, even though the temperature of the water topped 160 oF. And the microbes were not dead. No, they were happy as microscopic clams.

The adaptations that allowed the bacteria, dubbed Thermus aquaticus, to go about their business in the broiling heat of Yellowstone’s hot springs—and, it would eventually be revealed, other hot springs all around the world—changed scientists’ understanding of bacteria, but also the course of modern biology. In all the other bacteria known to science, such high temperatures destroyed the enzymes—molecular machines made of protein—that the bacteria used in day-to-day life. But T. aquaticus‘ enzymes managed the heat just fine, and 14 years after the bacterium’s discovery, in 1983, that tolerance would prove to be just what a chemist named Kary Mullis needed.

Mullis, who worked for Cetus Corporation in California, was driving along the highway one night when he realized that using a series of simple chemical steps, he could multiply a piece of DNA many times nearly automatically. The polymerase chain reaction, the process eventually perfected by Mullis’ colleagues at Cetus, is a crucial part of many modern experiments, most importantly the DNA sequencing like that used on crime scene shows or to reconstruct the evolutionary tree of life. With it, biologists can copy a scrap of DNA billions of times over the course of a few hours.

PCR starts out with the DNA in a tube with DNA polymerase, an enzyme that copies DNA, and the raw materials for the copying process. A biologist heats the tube up to about 98 oC, causing the two strands of the DNA to fall away from each other, and DNA polymerases latch onto each of the two halves. Using the raw materials, these enzymes build strands to match each of the halves they are clinging to just as they do when they’re in a cell. When they are done, there are two identical pieces of double-stranded DNA in the tube. When the tube heats up again, those halves fall apart and the DNA polymerases latch onto the four single strands, starting the process over.

The DNA polymerase has to be able to withstand the heat in the tube, though. And T. aquaticus‘ own DNA polymerase, known as Taq, could take temperatures of up to 98 oC without falling apart. Mullis used it in his reaction, which later won him the Nobel Prize. PCR’s importance in molecular biology is hard to overstate—it’s the lynchpin of most DNA technology out there—and the reaction has made millions of dollars for its patent holders. That night drive on the highway proved fruitful for Mullis (Taq polymerase, though, never made Yellowstone a cent, a fact that sparked some chagrin at the Park Service.)

Lately scientists interested in the bacteria that live in human homes have started a new chapter of research on Thermus aquaticus. As early as the 70s the bug was spotted living in hot water heaters. But it’s only been recently, since cheap DNA sequencing has made it possible to quickly and easily identify bacteria by their DNA, that microbial ecologists have started to try to map out their locations and learn more about how they live in man-made environments—discovering along the way, incidentally, that you may have some T. aquaticus in your tea. “It can live in your tea kettle, and that’s actually a great place to isolate Thermus from,” says Chris House, a professor of geosciences at University of Pennsylvania who has a call out for samples of hot water from houses across the country, in order to find out whether different flavors of the bacterium live in different geographic regions—in other words, what their biogeography, the geographic story recorded in their genes, is.

Findings from his study, which is still going on, may help explain how T. aquaticus gets into hot water heaters, tea kettles, and other comfortably hot indoor locations. If people near Yellowstone have the same variety of the bug in their hot water heaters as exists in the hot springs, that suggests that perhaps the heaters are being colonized from the hot springs somehow. And if all heaters in Manhattan share a specific kind, for instance, but heaters in Brooklyn have another, that suggests that perhaps plumbing companies carry the critter around.

These are the kinds of questions being asked today not just about Thermus aquaticus, but about many forms of invisible life. In a way it’s T. aquaticus that has made the recent surge in studies of microbial ecology possible. Thanks to its heat-hardy polymerase, and the DNA sequencing it helped create, the biogeography of its life and the rest of the living world is starting to come into better focus.

About the Author

Veronique Greenwood is a former staff writer at DISCOVER Magazine. She writes about everything from caffeine chemistry to cold cures to Jelly Belly flavors, and her work has appeared in Scientific American,,, and others. Follow her on Twitter here.