Thermophiles thrive in very hot environments. Archea in genus Sulfolobus live in sulfur-rich volcanic springs as hot as 90C. At temperatures this high, the cells of most organisms die because their DNA does not stay together in double helix, and many of their proteins denature. Sulfolobus and other extreme thermophiles avoid this fate because their DNA and proteins have adaptations that make them stable at high temperatures. One extreme thermophile that lives near deep-sea hydrothermal vents in the Pacific Ocean, Geogemma barossii, is informally known as "strain 21," since it can double its cell numbers even at 121C. Another extreme thermophile, Pryococcus furiosus, is used in biotechnology as a source of DNA polymerase for the PCR technique.