Geothermobacterium ferrireducens is a species of hyperthermophilic thermodesulfobacterium discovered and known exclusively from Obsidian Pool in Yellowstone National Park, Wyoming.

[1][2] Its name comes from the Latin ferrum, meaning Iron, and reducens, meaning conversion to a different state.

[3][2] The bacteria are gram-negative rods, and move using a single flagellum.

[2] They live in high temperatures, between 65 and 100 °C, with 85 to 90 degrees being the optimum range- the highest optimum temperature range of any member of the phylum Bacteria.

[2] They have an unusual biology: they do not require organic carbon for growth, instead growing by coupling hydrogen oxidation with a form of Fe(III) oxide reduction.