Abstract
We describe two species of hyperacidophilic, thermophilic, heterotrophic, aerobic archaea that were isolated from solfataric hydrothermal areas in Hokkaido, Japan. These organisms, Picrophilus oshimae and Picrophilus torridus, represent a novel genus and a novel family, the Picrophilaceae, in the kingdom Euryarchaeota and the order Thermoplasmales. Both of these bacteria are more acidophilic than the genus Thermoplasma since they are able to grow at about pH 0.