AST 309 part 2: Extraterrestrial Life Extreme Life on Earth Lessons for Astrobiology

Extremophiles are microbes that live in conditions that would kill other creatures. It was not until the 1970's that such creatures were recognized, but the more researchers look, the more they discover that most archaea, some bacteria and a few protists can survive in the harshest and strangest of environments. Archaea differ from bacteria primarily in that their cell wall does not contain a component called peptidoglycan.

Discovered in the 1970s in hot springs in Yellowstone National Park (right) and hydrothermal vents on the ocean floor. Grand Prismatic Spring in Yellowstone National Park. Some of the coloring is caused by extremophiles!

Thermophiles As of 2003, more than 50 species of thermophiles had been discovered. This bacteria survives in conditions of extreme heat; it can withstand water temperatures over 200 deg Fahrenheit and requires a temperature over 194 degrees Fahrenheit to survive. Thermophiles prevent the dissolution of cell wall constituents and genetic material at extremely high temperatures. Halophiles Halophilic bacteria thrive in an environment of extremely concentrated sodium, such as the Dead Sea or the Great Salt Lake. These bacteria can only survive in potassium chloride-rich environments.

Acidophile Acidophiles are found in highly acidic environments, where the pH level is below 5. At the opposite end of the spectrum, highly alkaline bacteria require a pH above 9. Extremely acidic bacteria are found in the runoff of mine drainage where the pH is below 1, more acidic than stomach acid. Anaerobophile The term anaerobic means in the absence of oxygen. Anaerobophiles die if any oxygen is present in their environments. One example of an anaerobic environment is the intestinal tract.

Psychophile Psychophiles thrive in the extremely low temperatures of ocean water, permafrost and polar ice. These bacteria contain special proteins that act as antifreeze. Barophile Barophile bacteria survive in extremely high gas or liquid pressure. These organisms live over 7,000 feet below the surface of the ocean, where pressure exceeds 3,160 pounds per square inch. Extremely low pressure extremophiles can be found in clouds. Radioresistant Extremophile Radioresistant extremophiles survive very high levels of radiation, over 1,000 times greater than a human cell can withstand. These bacteria are able to repair genetic mutations caused by radiation very quickly by disassembling mutated genetic sequences and putting them back together in proper sequence.

A sulfide-rich "black smoker" vents hot water into the cold ocean. Microbial extremophiles live on the vented minerals, anchoring a food chain of worms and other organism.

The habitable zone in our Solar System before discovery of extremophiles:

The habitable zone in our Solar System after discovery of extremophiles: