Today I am in the Yellowstone Park, and I wish I were dead
begins Rudyard Kipling in his letter. But for a man called Thomas D. Brock, Yellowstone Park has been a defining point in his career. Back in the 60s, biochemists have known for a long time that life cannot survive in high temperatures. The high energy from heat causes hydrogen bonds composing the secondary protein structure to break and denature the protein. The upper temperature limit for life was accepted to be 73°C. Brock however wasn't interested in setting an upper limit for life. During his field research in the Yellowstone Park in the 60s he discovered pink bacterial formation inside a hot spring with temperature of above 80°C. Because of his difficulty to cultivate the bacterium at such high temperature, Thomas D. Brock decided to study microorganisms from a different spring, with temperature ranging from 70°C to 73°C, which lead to the discovery of Thermus aquaticus. On September 5th, 1966 from a sample from Mushroom spring the culture YT-1 of T. aquaticus was isolated.
Mushroom spring (source: Brock. “Life at High Temperatures”. 1994)
This culture was the exact culture used as a source of Tac polymerase for PCR.
Polymerase chain reaction, or PCR, is a technology used to amplify a single or multiple copies of DNA. It’s capable of generating thousands to millions copies of the DNA sequence of interest. According to Brock the PCR technology that was derived from his discovery of T. aquaticus is so important that Hoffmann-LaRoche, a Swiss pharmaceutical giant, paid more than $300 million to acquire world rights for the process. What links the discovery of a microorganism to a multimillion-dollar industry?
The man behind modern day PCR is Kary Banks Mullis of Cetus Corp. His idea was to use primers to bracket DNA sequence of interest, and to copy it using DNA polymerase allowing for rapid multiplication of very small quantities of genetic material. PCR is a process that consists of many repeated cycles of temperature change. At very high temperatures, 94°C to 98°C, DNA begins to “melt” and hydrogen bonds joining complementary bases between the 2 strands begin to break. The temperature is then lowered to 50-65 °C which allows annealing of primers to the template strains of DNA. It’s very important that the temperature is low enough to allow the formation of hydrogen bonds, but it also needs to be high enough so that only the corresponding bases bind. This is followed by an elongation step and the temperature is set accordingly to the polymerase being used. Each DNA polymerase has its own optimum activity temperature. As a rule of thumb, at its optimal temperature, a DNA polymerase can polymerase as much as 1000 bases per minute. This means that using PCR a small piece of genetic material can be amplified across several orders of magnitude in a short period of time. However, DNA polymerase previously used was being destroyed at each replication cycle, and had had to be constantly replaced, which is expensive. But where does Tac polymerase fit into all of this? Tac polymerase is an enzyme isolated from T. aquaticus. Due to the microorganisms nature, the polymerase extracted from it can withstand very high temperatures without denaturing, thus eliminating the need to constantly replace the enzyme after each PCR cycle making the process much more affordable. This has made the process a part of multimillion dollar industry and has various applications ranging from early detection of diseases to forensic sciences. In 1993 Kary Mullis received a Nobel Prize in Chemistry in recognition of his improvements of PCR.
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