In 1976, Alice Chien biochemically characterized the DNA polymerase of Thermus aquaticus, the thermophilic bacterium isolated by Thomas Brock in the hot springs of Yellowstone National Park in 1969. The resulting enzyme — known as Taq polymerase — retained activity above 90°C, the temperature needed to separate DNA strands in each PCR cycle. Without this property, Mullis's original PCR (1983) required manually adding fresh polymerase each cycle, making it impractical. Integration of Taq into the PCR protocol by Saiki et al. (1988) transformed the technique into a fully automatable process.