Plumes of hot water gush upward from chimney-like structures in the floor of the mid-Atlantic Ocean, turning black as the sulfide minerals they contain mix with the cold surrounding water. Known as black smokers, such hydrothermal vents are signs that the violent, molten world that exists beneath Earth’s surface is still very much active. And amazingly, alive within this mercurial environment, is a microorganism known as Pyrolobus fumarii, the “fire lobe of the chimney.”
P. fumarii was discovered in 1997 by German microbiologist Karl O. Stetter and colleagues in the wall of a black smoker nearly 12,000 feet below the ocean’s surface in the Mid-Atlantic Ridge. The organism, engulfed by hot water and concentrations of sulfide minerals that would be toxic to most other life forms, thrived in the smoker’s extreme environment, living the lifestyle characteristic of an extremophile.
But P. fumarii is no ordinary extremophile, if such a thing can be said to exist. Indeed, it is unique from all other life forms in that it holds the record for the highest temperature -- 235 °F -- at which life has been found to survive. Its rate of grow and reproduction is optimal at about 223 °F. These characteristics make it a champion among hyperthermophiles, organisms that thrive at temperatures of 140 °F or higher.
P. fumarii also endures pressures of as much as 250 bars, or about 3,625 pounds per square inch (psi). For comparison, humans and other terrestrial animals living at sea level experience a pressure of only 14.7 psi. And unlike us, P. fumarii gets by on a diet of inorganic chemicals, hydrogen, and carbon dioxide found in the walls of black smokers. This mode of metabolism, called chemolithoautotrophy, enables P. fumarii to extract all the energy it needs from its habitat.
Such tolerance of extremes suggests that P. fumarii possesses extraordinary adaptations known only to the archaea, a group of single-celled, primitive organisms that have unique molecular traits distinguishing them from closely related bacteria. Archaea are known for their extreme lifestyles, for pushing the boundaries of life on Earth. They have been found in environments characterized by extreme temperatures, by high salinity and acidity, by the near complete absence of oxygen, and by the abundance of a specific chemical or compound, such as arsenic or methane, respectively. Archaea occur in other environments, too; for example, methanogenic (methane-producing) archaea have been isolated from the human gut and oral cavity.
Genome sequencing has revealed that P. fumarii's unique adaptations stem from its genetic constitution. A relatively large number of the approximately 2,000 or so genes in its genome share little or no similarity with genes discovered in other microorganisms. Hence, P. fumarii’s genome may be tailored specifically for life in extreme heat.
The extraordinary diversity and adaptations of archaea like P. fumarii have rendered these organisms especially important to science. Understanding their biochemical properties, for example, is a key component of investigations concerning the origin of life on Earth and the search for extraterrestrial life. Indeed, at the extreme biochemical limits of life on Earth lie secrets containing vital clues -- potentially vast amounts of information -- about different environmental conditions capable of supporting life, which could tell us where, beyond our plant, life may exist.
Kara Rogers is a freelance science writer and senior editor of biomedical sciences at Encyclopaedia Britannica, Inc. She is a member of the National Association of Science Writers and author of Science Up Front on the Britannica Blog. She holds a Ph.D. in Pharmacology/Toxicology, but enjoys reading and writing about all things science. You can follow her on Twitter at @karaerogers.
This post also appears on the Britannica Blog.