A variety of microorganisms grow in physically or geochemically severe conditions. Microorganisms are generally classi’ed into four groups on the basis of the temperature at which they grow: psychrophiles, mesophiles, thermophiles, and hyperthermophiles. Hyperthermophiles, which grow optimally at temperatures greater than 80°C, are found in hot environments such as deep-sea vents, submarine hydrothermal areas, and continental solfataras.1 In the late 1960s, the ’rst hyperthermophiles, Sulfolobus sp., were discovered in a hot acidic spring in Yellowstone National Park.2 Since then, more than 50 hyperthermophile species have been discovered and it has been reported that a hyperthermophile can survive even at 122°C.3 Most hyperthermophiles are members of the Archaea (e.g., Thermococcus, Pyrococcus, and Sulfolobus) and some bacterial hyperthermophiles (Thermotoga and Aquifex) have been discovered.