Some like it hot

The hot springs and geysers of Yellowstone National Park in the USA have fascinated tourists and scientists for many years. But it was not until 1964 that microbiologist Thomas Brock tested for microbial life in waters as hot as 82°C. He found what are now called thermophilic bacteria, astounding micro-organisms thriving in high temperatures that would denature the enzymes of most other life forms. This inspired others to search for microbes in inhospitable environments. It also facilitated a vital technique in molecular biology, the polymerase chain reaction, or PCR, for copying small amounts of DNA.

The PCR reaction mixture contains DNA nucleotides, DNA polymerases and some other ingredients. It is heated to 90°C, causing the double-stranded DNA to separate into two single strands. Then it is cooled slightly and the DNA polymerase makes complementary strands of DNA. The mixture is reheated and the process continued, with the amount of DNA doubling each cycle. The DNA polymerase of most organisms is denatured at 90°C, so new DNA polymerase needs to be added for each cycle. However, DNA polymerase from thermophilic bacteria is made to order and, because DNA structure is identical in all living beings, it applies to any DNA. Kary Mullis perfected PCR in 1983, later receiving a Nobel Prize. The first DNA polymerase used widely in PCR (commercially known as Taq-polymerase) came from Thermus aquaticus, a thermophilic bacterium isolated by Brock.