Extremophiles
Definitions
Types
Clues to the origin of life
Readings:
1) Wikipedia links: “Extremophile” and “Panspermia”
2) Life on the edge: Adventures of an extremophilic scientist: Darlene Lim
3) Madigan & Marrs, Extremophiles. Scientific American, April 1997
What are “extremophiles” and
where do you find them?”
Extremophiles
“Odd forms of life in out of the way places”
http://www.starwarsholidayspecial.com/images/photos/cantina/cantina_denizens_4.jpg
“Classic” definition:
• A microorganism in the Domain Archaea that thrives
under extreme environmental conditions
(temperature, pH, salinity) – Oxford Dictionary of Ecology
The three “domains” of life - Madigan & Marrs, 1997)
Extremophile sub-types according to Wikipedia:
“There are many different classes of extremophiles, each corresponding to
the way its environmental niche differs from mesophilic conditions. These
classifications are not exclusive. Many extremophiles fall under multiple
categories. For example, organisms living inside hot rocks deep under
Earth's surface are both thermophilic and barophilic.”
Acidophile
Alkaliphile
Endolith (cryptoendoliths)
Halophile
Hyperthermophile
Hypolith
Lithoautotroph
Metalotolerant
Oligotroph
Osmophile
Piezophile
Polyextremophile
Psychrophile/Cryophile
Radioresistant
Thermophile
Thermoacidophile
Xerophile
http://en.wikipedia.org/wiki/Extremophile#Types_of_extremophiles
Sub-groups of Extremophiles
•
•
•
•
•
•
Thermophile
Hyperthermophile
Psychrophile
Acidophile
pH
Alkaliphile
Halophile - salt
Temperature
Thermophilic bacteria coloring the hot
springs of Yellowstone Park.
http://en.wikipedia.org/wiki/Extremophile#Types_of_extremophiles
Salt Ponds in San Francisco Bay
http://earthobservatory.nasa.gov/IOTD/view.php?id=4877
Salt Ponds in San Francisco Bay
These ponds are colored by halophilic
bacteria that thrive in the hyper-saline
environment of these salt evaporation ponds.
http://en.wikipedia.org/wiki/File:Salt_ponds_SF_Bay_(dro!d).jpg
http://www.environmentalgraffiti.com/featured/san-francisco-incredible-stained-glass-salt-ponds/14109
Broader definitions:
An “Extremophile” can be any organism found in
extreme environments (not just archaebacteria)
Tardigrades (Phylum Tardigrada) are microscopic animals (>1000 spp.)
that are found from the Himalayas to the deep seas, and from the
equator to the poles.
Tardigrades are polyextremophiles and are able to survive in extreme environments
that would kill almost any other animal. Some can survive temperatures of -273°C,
close to absolute zero, temperatures as high as 151 °C (303 °F), 1,000 times more
radiation than other animals such as humans, almost a decade without water , and
even the vacuum of space. In September 2007, tardigrades were taken into low Earth
orbit on the FOTON-M3 mission and for 10 days were exposed to the vacuum of space.
After they were returned to Earth, it was discovered that many of them survived and
laid eggs that hatched normally, making these the only animals shown to be able to
survive the vacuum of space.
http://en.wikipedia.org/wiki/Tardigrade
Temperature and light penetration with depth further affect productivity and the
distribution of organisms
“pelagic”
“benthic” = bottom
“abyssal”
Fig. 3.6
Molles & Cahill, 2008
An ecosystem of chemotrophic organisms at the bottom of the ocean.
Molles & Cahill 2008
Creatures of the deep!
Molles & Cahill 2008
Science, 8 January, 2010
What can we learn from
extremophiles?
• Alternate biochemical and physiological
adaptations
– novel enzymes
– Alternate biochemical pathways (chemosynthesis)
• Clues to the origin of life.
Is the Earth unique?
As far as we know, the Earth is the only planet where life exists.
It is highly unlikely that life (as we know it) exists on other planets
in our solar system.
(“Goldilocks” Explanation)
Are other extreme forms of life (“extremophiles”) possible?
What about life on other planets in other solar systems in other
galaxies?
What is life anyway?
Organization (low entropy, high information content)
Energy transfer, metabolism
Comprised of cells, membranes
Replication – reproduces on its own
Information content (DNA, RNA…)
Carbon-based
Composed of 25 elements
(esp. Carbon, Hydrogen, Nitrogen, Oxygen, Phosphorus, Sulfur)
When and how did life originate?
Evidence for Early Life
3.85 BYA – Evidence from Molecular evolution (early life was hot and
chemotrophic)
3.8 BYA – Geological evidence
(organic deposits in earliest sedimentary rocks)
3.5 BYA – Possible fossil bacteria with organic inclusions
3.2 BYA – Filamentous microfossils
3.0 – 2.7 BYA – Developed bacterial communities
(photosynthetic stromatolites)
Earth’s Early Life Forms
Raven & Johnson 1992
Campbell & Reece 2002
“Biological Clock”
˜4.6
BYA
˜3.8
BYA
˜3.5
BYA
Raven & Johnson 1992
Theories regarding life’s origins:
“Primordial soup” (Miller and Urey’s experiments)
“Panspermia” – “seeding” of organic compounds or organisms
from space (analysis of organic molecules in meteorites)
Evidence regarding the early Earth and life’s origins
Early conditions (first 800 MY) were hostile to “life as we know it”
bombardment from outer space (accretion)
extremely hot
volcanic activity – release SO2
no atmosphere
Later conditions
early atmosphere – lots of CO2, no O2, O3
bombardment from outer space
Campbell & Reece 2002
Earth’s Early Energy Sources
The early Earth was a
harsh environment,
unsuitable for most
modern-day organisms
(except certain
extremophiles?)
Raven & Johnson 1992
The Miller and Urey Experiment (1953) – organic molecules can be made from inorganic
ones under the right conditions (believed to resemble the early Earth).
Raven & Johnson 1992
Life abounds in the stranges places…thermal hot springs
Campbell & Reece 2002
… deep sea vents
Campbell & Reece 2002
Theories regarding life’s origins:
“Primordial soup” (Miller and Urey’s experiments)
“Panspermia” – “seeding” of organic compounds or organisms
from space (analysis of organic molecules in meteorites)
Panspermia Hypothesis – the “seeds” of life exist throughout the
universe (perhaps as extremophiles!). The Earth was “seeded” by
life arriving from space (also called “Exogenesis”).
http://en.wikipedia.org/wiki/Panspermia
ALH84001 – the “Mars Meteorite”
Mars
First reported in McKay et al. 1996, Science 273:924-930
as recounted by A. Tremain at:
http://www.lpi.usra.edu/lpi/meteorites/life.html
Carbonate Inclusions in ALH84001 – consistent with biochemical processes
http://www.lpi.usra.edu/lpi/meteorites/life.html
Possible Bacterial Fossils in ALH84001
http://www.lpi.usra.edu/lpi/meteorites/life.html
Possible Bacterial Fossils in ALH84001
http://www.lpi.usra.edu/lpi/meteorites/life.html
Possible Bacterial Fossils in ALH84001 – Did life on Earth originate this way?
http://www.lpi.usra.edu/lpi/meteorites/life.html