Pyrolobus fumarii (Latin for "fire lobe of the chimney"[1]) is a species of archaea known for living and reproducing at extremely high temperatures that kill most organisms.

It was first discovered in 1997 in a black smoker hydrothermal vent at the Mid-Atlantic Ridge, setting the upper-temperature threshold for known life to exist at 113 °C (235.4 °F) with an optimal temperature of 106 °C.

A study found that P. fumarii contained capabilities of growing by thiosulfate reduction, however, with NH4Cl present, the archaea growth resulted in a fivefold yield.

[2] For P. fumarii reduction of succinyl-CoA, which is used in the process of generating energy in the cell, does not rely on NAD(p)H but instead requires reduced methyl viologen.

[4] P. fumarii structure contains an S-layer, commonly found in non-lab prokaryotic strains, which stimulates a pore with a depression in the middle.

[6] Understanding the ability of P. fumarii to withstand high temperatures and its genome capabilities to be thermostable and heat-tolerant could lead to many pharmaceutical, agricultural, and industrial applications.