Thermus aquaticus

**Thermus aquaticus** (Latin for "hot water") is a heat-loving bacterium from the Deinococcota phylum. It is best known as the original source of Taq DNA polymerase, a heat-stable enzyme that became essential for the polymerase chain reaction (PCR), a technique that revolutionized molecular biology by allowing rapid DNA amplification.

**History**

In the 1960s, scientists studying hot springs assumed no bacteria could survive above about 55 °C. That assumption was quickly overturned as researchers found many bacteria thriving in even hotter waters. In 1969, Thomas D. Brock and Hudson Freeze of Indiana University described a new thermophilic species, *Thermus aquaticus*, first isolated from Mushroom Spring in Yellowstone National Park’s Lower Geyser Basin, near Great Fountain Geyser and White Dome Geyser. The bacterium has since been found in similar hot environments worldwide.

Decades later, this discovery proved pivotal. Biochemist Kary Mullis, working at Cetus Corporation, invented PCR, a technique that transformed DNA research and earned him the 1993 Nobel Prize in Chemistry. PCR enabled major advances in medical diagnostics, genetics, and other fields. After Mullis’s discovery, Cetus awarded him $10,000. However, Cetus later sold the PCR patent to F. Hoffmann-La Roche for $300 million—a deal Mullis felt cheated by for the rest of his life. Roche has since generated enormous revenue from PCR, with annual sales reaching $5.4 billion in 2022. Despite these profits, neither the National Park Service, Yellowstone National Park, nor the state of Wyoming received any share. Recognizing the scientific and commercial potential of Yellowstone’s extremophiles, biotechnology companies like Diversa signed bioprospecting agreements with the Park Service, leading to further exploration and applications, though not without environmental concerns. Brock’s original discovery in Yellowstone’s hot springs ultimately drove major scientific breakthroughs, highlighting how basic research can fuel innovation.

**Biology**

*T. aquaticus* grows best at 65–70 °C but can survive between 50 °C and 80 °C. It primarily obtains food by scavenging proteins from its surroundings, as shown by its many extracellular and intracellular proteases, peptidases, and transport proteins for amino acids and oligopeptides. It is a chemotroph, performing chemosynthesis, but because its temperature range overlaps with that of photosynthetic cyanobacteria, it sometimes lives alongside them, using energy from their photosynthesis. Normally aerobic, one strain (*T. aquaticus* Y51MC23) can also grow anaerobically. Its genome consists of one chromosome and four plasmids, and sequencing revealed two complete and two partial prophages, plus numerous CRISPR loci.

**Morphology**

*T. aquaticus* is generally cylindrical, 0.5–0.8 μm in diameter. Shorter rods are 5–10 μm long; longer filaments can exceed 200 μm. It can appear as rods or short filaments in different cultures. Rod-shaped cells tend to aggregate, sometimes forming spherical bodies 10–20 μm across, called rotund bodies. These are not made of cell envelope or outer membrane, as once thought, but from remodeled peptidoglycan cell wall. Their exact role is unknown, but they may store food or nucleotides, or help with colony attachment and organization. *T. aquaticus* is a typical gram-negative bacterium, with less peptidoglycan than gram-positive species. In sunlight, it can appear yellow, pink, or red—colors visible in hot springs. It may have flagella for movement or be immotile.

**Enzymes from *T. aquaticus***

The bacterium is famous for its thermostable enzymes, especially Taq DNA polymerase.

**Aldolase** – In 1970, Freeze and Brock described a heat-stable aldolase from *T. aquaticus*, part of early efforts to understand how enzymes work at high temperatures.

**RNA polymerase** – In 1974, Alice Chien Chang and colleagues isolated the first polymerase from *T. aquaticus*: a DNA-dependent RNA polymerase involved in transcription.

**Taq I restriction enzyme** – Most molecular biologists likely first encountered *T. aquaticus* in the late 1970s or early 1980s, when useful restriction endonucleases were isolated from it. The shorthand “Taq” came from the convention of naming restriction enzymes after the genus and species of the source organism.

**DNA polymerase (“Taq pol”)** – DNA polymerase was first isolated from *T. aquaticus*.