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: