The Rushing Fireball
In 1986, German microbiologists Karl Stetter and Gerhard Fiala were investigating the geothermally heated marine sediments off the beach of Porto Levante on Vulcano Island. From this extreme environment, with temperatures between 90°C and 100°C, they isolated a new species of Archaea, a domain of single-celled organisms. They named it Pyrococcus furiosus, meaning "rushing fireball," to describe its spherical shape and its rapid swimming and reproduction. This organism is a hyperthermophile, an extremophile that thrives in extremely hot environments. Its optimal growth temperature is 100°C (212°F), a temperature that would instantly destroy most other forms of life.
P. furiosus is a strict anaerobe, meaning oxygen is toxic to it. It lives in anoxic volcanic mud and makes a living as a heterotroph, feeding on sugars and proteins in the sediment. Under these boiling conditions, it has a remarkable doubling time of just 37 minutes. The organism's genome, sequenced in 2001, consists of 1,908 kilobases and codes for 2,065 proteins. Many of these proteins are exceptionally heat-stable, a property that attracted intense interest from molecular biologists.
A Higher-Fidelity Photocopier
The invention of the Polymerase Chain Reaction (PCR) in the 1980s was a major advance, allowing scientists to make millions of copies of a specific DNA segment. Initially, the process was cumbersome. It required a DNA polymerase enzyme that was destroyed during the high-temperature step (around 95°C) needed to separate the DNA strands. Researchers had to add fresh enzyme during every cycle. The discovery of Taq polymerase from the Yellowstone bacterium Thermus aquaticus solved this by providing a heat-stable enzyme. However, Taq polymerase makes frequent errors, roughly one mistake for every 9,000 base pairs it copies.
This is where Pyrococcus furiosus from Vulcano changed everything. Scientists isolated its DNA polymerase, now known as Pfu polymerase. Pfu polymerase is very thermostable—remaining 95% active after an hour at 98°C—but it also has a "proofreading" ability. It possesses a 3' to 5' exonuclease activity, which is like a backspace key. When it adds an incorrect nucleotide to the growing DNA strand, it can detect the mistake, remove the error, and insert the correct one. This proofreading function makes Pfu polymerase far more accurate than Taq. Its error rate is about 1 in 1.3 million base pairs. This high fidelity is essential for applications like gene cloning, sequencing, and diagnostics, where accuracy is important.