Download Phys 214. Planets and Life

Phys 214. Planets and Life
Dr. Cristina Buzea
Department of Physics
Room 259
E-mail: [email protected]
(Please use PHYS214 in e-mail subject)
Lecture 18. Life at the extremes. Part I.
February 25th, 2008
Contents
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Textbook pages 178-181
& the latest research in the field
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Life at the extreme. Part I.
Temperature extremes - High temperature
Life at the extreme
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Organisms on Earth have different type of metabolisms and use different carbon sources
Scientists recently discovered that life can be found in most unlikely places on Earth!
An extremophile is an organism that thrives under "extreme" conditions.
The term “extremophile” is relatively anthropocentric (in the eye of the beholder), we judge it
compared to human extremes!
e.g. we use O2 but for many organisms O2 is poisonous
Extreme environments
High sugar concentrations - Osmophillics
Low carbon environment - Oligotroph
Subsurface rocks environments - Endoliths
Bacteria revived after being frozen 32,000
years (Pleistocene age)!
Bacteria that survived the trip to the Moon
and back!
Polyextremophile - organism which
combines several extremophilic features.
Temperature
Temperature limits for life. The
highest and lowest temperature for
each major taxon is given. Archaea are
in red, bacteria in blue, algae in light
green, fungi in brown, protozoa in
yellow, plants in dark green and
animals in purple.
(NATURE | VOL 409 | 22
FEBRUARY 2001)
Complex organisms (Eukarya) occupy a more restrictive thermal range than Bacteria and Archaea.
Eukaryotic organisms are not known to live above 60oC.
However, eukaryotes can be found in environments of great acidic, salt concentration, high pressure, toxic
metals.
Temperature
Liquid water and life on planets.
Temperature scale for the presence of
liquid water on Earth and for the
observed enzyme activity and growth
of microorganisms (Bacteria and
Archaea).
High Temperatures
Yellowstone National Park, Geothermal area in El Tatio Chile, Deep sea hydrothermal vents
Thermophiles – heat-loving extremophiles; optimum growth temperature between
50-70°C or more, and a minimum of about 20 °C.
Environment: geothermally heated regions of the Earth: hot springs (Yellowstone
National Park), and deep sea hydrothermal vents.
1) Obligate thermophiles (extreme thermophiles) require very high temperatures for
growth
2) Facultative thermophiles (moderate thermophiles) can thrive at high temperatures
but also at lower temperatures (below 50 °C).
3) Hyperthermophiles are particularly extreme thermophiles for which the optimal
temperatures are above 80 °C.
Hyperthermophiles
Red coloration on rocks near Naples,
Italy, produced by the hyperthermophile
Sulfolobus solfataricus.
Hydrothermal vents
Yellowstone National Park hot spring. Orange
and brown microbial mats of hyperthermophilic
bacteria and archaea.
Hyperthermophiles- require a very high temperature for growth (60 °C to 113 °C). also able to
withstand other environmental extremes such as high acidity or radiation levels.
Environment: hot, sulfur-rich environments usually associated with volcanism, such as hot
springs, geysers and fumaroles, hydrothermal vents.
Many Archea hyperthermophiles require elemental sulfur for growth.
Some are anaerobes -use the sulfur as an electron acceptor during respiration instead of oxygen.
Some are lithotrophs that oxidize sulfur to sulfuric acid as an energy source, thus requiring the
microorganism to be adapted to very low pH (i.e. it is an acidophile as well as thermophile).
Hyperthermophiles
Discovered in the 1960s, in hot springs in Yellowstone National Park. Since then, more than
fifty species have been discovered.
Domain: Archaea (majority), Bacteria (some cyanobacteria and anaerobic photosynthetic
bacteria grow well at 70 to 75°C.
Pyrolobus fumarii (Archaea) 113°C in Atlantic hydrothermal vents.
Methanopyrus kandleri (Archaea) in 80–100°C in a Gulf of California vent.(special interest
because of its ancient genetic make-up -may have been among the earliest organisms on
Earth!)
Pyrococcus furiosus (Archaea) thrives at 100°C, Italy near a volcanic vent.
Aquifex aeolicus (Bacteria) 85–95°C in Yellowstone National Park.
The most heat-tolerant hyperthermophile is the recently-discovered Strain 121 which has
been able to double its population during 24 hours in an autoclave at 121°C (hence its
name). (An autoclave is a pressurized device designed to heat aqueous solutions above their
boiling point to achieve sterilization.)
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The ability to grow at 121 degrees Celsius is significant because medical equipment is
exposed to this temperature for sterilisation in an autoclave. Prior to the 2003 discovery
of Strain 121, a fifteen-minute exposure to autoclave temperatures was believed to kill
all living organisms.
The upper temperature for life is still to be determined! There is evidence of intact
microorganisms with DNA and RNA in hydrothermal vent sulfides at temperatures
exceeding 200oC.
Hyperthermophiles
Beppu hot spring, Japan.
Phylogenetic tree
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Sulfolobus tokodaii (Archaea) grows optimally at 80 degrees Celsius in an acidic,
sulfur-rich environment.Has 14 genes that resemble those in eukaryotes, never
found in other archaea before -> of all sequenced archaea to date, S. tokodaii is the
one most closest related to eukaryotes.
Thermophilic organisms populate the deepest branches of the phylogenetic tree –
suggesting that they are in the evolutionary sense closest to the origin of life.
Hyperthermophiles
What happens at high temperatures to most organisms?
At temperature above 100oC most organisms cease to function.
100oC is the boiling point of water is not significant!
This temperature corresponds to the thermal content that denatures the essential polymers!!
Temperatures above 75oC are a problem for many photosynthesizers because chlorophyll
degrades under such conditions.
Solubility of oxygen and carbon dioxide drops significantly as temperature increases.
Aquatic organisms that rely on oxygen or carbon dioxide will not survive.
E.g. Fish expire above 40oC for this reason.
A. Above 150°C the cohesion of DNA and other vital molecules begins to break down.
B. The intolerance of most organisms for extreme heat comes from the nature of polypeptide
folding - proteins unfold and are unable to perform their functions. Above about 100oC
many proteins denature.
C. The fluidity of the membrane is increased so much that cells cannot control the input or
output of molecules.
Hyperthermophiles
Adaptation:
Theoretically,the temperature effects should be compensated with either higher pressure or
with increasing salt concentration.
A1. Some organisms ingest or produce salts (KCl, MgCl2) which enhance the stability of the
DNA chain by partially canceling out the negative charges of the phosphate groups in
the nucleic acid backbone.
A2. All hyperthermophiles have a protein (reverse gyrase) that positively supercoils DNA,
witch along with cationic proteins increases the thermal stability of DNA.
B. The protein molecules of hyperthermophiles can maintain structural stability (and
therefore function) at high temperatures. Such proteins have evolved to exhibit optimal
function at much greater temperatures.
heat stable proteins - proteins resistant to unfolding - more densely packed to exclude
internal water, and more hydrophobic, have more salt bridges, with more bonds between
polypeptide chains to provide sturdiness. (The enzyme amylopullunase does not
denature even at temperatures of 140oC.)
C. Membranes - different proportion of saturated (no double or triple bonds with carbon)
versus unsaturated fats, which optimized membrane stability at high temperature.
Therefore, fundamental changes in protein and lipid structure compensate for increased
mobility and fluidity at high temperatures.
Hydrothermal vents
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Hydrothermal vents are underwater oases, providing habitat for
many creatures that are not found anywhere else in the ocean.
More than 300 new species have been identified since 1977.
Vents form where the planet's crustal plates are slowly spreading
apart and magma is coming up from below to form mid-ocean
ridges.
As cracks form at these spreading centers, seawater seeps a mile or
two down into the hot rock.
Enriched with minerals leached from the rock, the water heats and
rises to the ocean floor to form a vent.
Water pouring out of vents can reach temperatures up to about
4000C; the high pressure keeps the water from boiling.
However, the intense heat is limited to a small area. Large
temperature gradient - within less than an inch of the vent opening,
the water temperature drops to 2 C, the ambient temperature of
deep seawater.
Most of the creatures that congregate around vents live at
temperatures just above freezing. Thus chemicals are the key to
vent life, not heat!
harsh combination of toxic chemicals, high temperatures, high
pressures, and total darkness at these vents.
Hydrothermal vents
Pink jellyfish from (Stauromedusae) and spiky tubeworm near the newly
discovered Medusa hydrothermal vent field. NSF
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Tube worms.
The most hardy hyperthermophiles yet discovered live on the superheated walls of deepsea hydrothermal vents, requiring temperatures of at least 90°C for survival
The giant tube worm - the most striking members of a diverse community that forms
around hydrothermal vents. Besides giant tube worms (found only in the Pacific), there
are pencil-size worms with accordion-like tubes.
Biologists have observed a variety of smaller crustaceans around vents, including
miniature lobsters, sea anemones, snakelike fish, and even octopuses.
While octopuses are at the upper end of the vent's food chain, bacteria are at the bottom.
Hydrothermal vents
Snails, fish, crabs living near deep sea vents.
http://www.soest.hawaii.edu/expeditions/mariana/dailyupdates-39.htm
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Chemosynthetic Bacteria
Mussels, shrimp, clams, and crabs are abundant at many vents, but these are not the
same species that you find in seafood dishes.
The cocktail-size shrimp that dominate vents in the mid-Atlantic, for example, have no
eyes. However, at least one species has an extremely sensitive receptor on its head that
may be used to detect heat or even dim light coming from vents.
Scientists still aren't sure how shrimp and other vent creatures cope with chemicalloaded seawater that would kill ordinary shellfish.
The most prevalent chemical dissolved in vent water is hydrogen sulfide, which smells
like rotten eggs. This chemical is produced when seawater reacts with sulfate in the
rocks below the ocean floor. Vent bacteria use hydrogen sulfide as their energy source
instead of sunlight. The bacteria in turn sustain larger organisms in the vent community.
Hydrothermal vents
Tube worms
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Brisingid sea stars in the Lau Basin
Iwa hirsute, the Yeti crab - blind
creature has the vestige of a
membrane instead of eyes.
The clams, mussels, tube worms, and other creatures at the vent have a symbiotic
relationship with bacteria. The giant tube worms, for example, have no digestive system
- no mouth or gut. The worm depends virtually solely on the bacteria for its nutrition.
The brown, spongy tissue filling the inside of a tube worm is packed with bacteria about 285 billion bacteria per ounce of tissue.
The plumes at the top of the worm's body are red because they are filled with blood,
which contains hemoglobin that binds hydrogen sulfide and transports it to the bacteria
housed inside the worm. In return, the bacteria oxidize the hydrogen sulfide and convert
carbon dioxide into carbon compounds that nourish the worm.
High temperature -large organisms
Pompeii Worm, Alvinella pompejana
Pompeii Worm - the most heat-tolerant animal on Earth.
reside in tubes near hydrothermal vents along the seafloor.
5 inches in length and are pale gray with red tentacle-like gills on their heads.
Their tail end is resting in temperatures as high as 80º C, while their feather-like head sticks
out of the tubes into water that is a much cooler 22º F.
Chemolithotrophic Bacteria form a "fleece-like" covering on their backs - living in a
symbiotic relationship, the worms secrete mucous from tiny glands on their backs to
feed the bacteria, and in return they are protected by some degree of insulation.
Next lecture
Extremophiles part II.
Quiz. 10 minutes