Picrophilus
In taxonomy, Picrophilus is an archaean genus of the family Picrophilaceae. "Picrophilus" is an extremely acidophilic genus within Euryarchaeota. These microbes are the most acidophilic organisms currently known, with the ability to grow at a pH of less than 0.5. They were first isolated from samples taken from acidic hot springs and dry hot soil in Hokkaido (Japan). They are obligate acidophiles and are unable to maintain their membrane integrity at pH values above 4. While phylogenetically related to other organisms within Thermoplasmata, unlike "Thermoplasma" and "Ferroplasma", "Picrophilus" contains an S-layer cell wall.