Aquificae bacteria

Aquificae (Aquifex or Hydrogenbacter) bacteria have been isolated from hot springs, volcano calderas, and marine hydrothermal vents. These bacteria thrive at 86-95°C, making them some of the most thermophilic bacteria known. Members of this group appear to be restricted to geothermal habitats, where they live by splitting hydrogen gas of hydrogen sulfide and fixing carbon dioxide for carbon.

The Aquificae include halophiles, isolated from saline hot springs, and an acidophile, isolated from an acidic sulfur deposit. The best characterized are species of Aquifex, a blue filament bacteria.

References:
Assembling the tree of life By Joel Cracraft, Michael J. Donoghue