Transcript ppt

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 19. Life at the extremes. Part II
February 27th, 2008
Contents
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Life at the extremes
Low-temperatures
High-salinity
Low 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)
Ostrocods = small crustaceans
(1 mm size), protected by a
bivalve-like "shell".
Protozoa = one-celled eukaryotes.
Algae = diverse group of simple plant-like organisms,
unicellular to multicellular. The most complex seaweeds; they lack the distinct organs of higher plants
such as leaves and vascular tissue.
Complex organisms (Eukarya) occupy a more restrictive thermal range than Bacteria and Archaea
Low temperature - Psychrophiles
Subglacial stream - Glacier du Mont Mine, Swiss Alps.
Psychrophiles - extremophiles capable of growth and reproduction at or below 15 oC.
Environments ubiquitous on Earth - alpine and arctic soils (permafrost), high-latitude and deep ocean
waters, arctic ice, glaciers, snowfields, & refrigerated appliances.
1) Obligate psychrophiles - have optimum growth temperature of 15°C or lower and cannot grow in a
climate hotter than 20°C. (Antarctica or at the freezing bottom of the ocean floor)
2) Facultative psychrophiles - can grow at 0°C up to ~ 40°C, and exist in much larger numbers than
obligate psychrophiles.
Many phychrophiles are polyextremophiles:
The ones living in deep ocean waters -> extremely high pressures
Organisms in sea ice are exposed to high salt concentrations.
On snow, glaciers, polar surface organisms are exposed to strong UV radiation.
Organisms found in rocks in Antarctic dry deserts - low water and nutrients.
Psychrophiles
Universal phylogenetic tree features hyperthermophilic (grow >90o), and cold adapted species –
phychrophilic (blue lines), or psychrotolerant (violet lines) of Bacteria and Archaea. Permanently
cold habitats would favour the evolution of obligate phychrophiles.
Psychrophiles are well represented by all three domains of life, Bacteria, Archaea, &
Eukarya. Obligate psychrophiles have evolved only among the Bacteria.
Many Eukaryotes: Diatoms, Lichens, Nematodes (Panagrolaimus davidi), Antifreeze Fish
(Paraliparis Devriesi), Tardigrades, Himalayan midge.
Psychrophiles
South Pole bacteria. NSF
•(Brine is water saturated or
nearly saturated with salt)
(Planets and life, Sullivan and Baross)
Psychrophiles
At very low temperatures the water becomes ice.
However, small amounts of liquid water are available for life
in different types of ice formations, especially at brine
inclusions. Water can remain liquid at temperatures lower
than -30oC in the presence of salts and other solutes.
Many species of snow algae were observed on Alaskan
glaciers (green algae and cyanobacteria).
Some of them produce brilliant colored spores. They alter the
albedo of the snow and induce snowmrlt, incresing the
availability of liquid water.
Some organisms produce extra-cellular enzymes that lead to
pitting of ice.
Microorganisms are abundant in frozen environments.
Possibility of life on Mars, and other icy bodies?
(brine = water saturated or nearly saturated with salt)
(albedo = the extent to which it diffusely reflects light from the
sun)
Chlamydomonas nivalis
This is most well-known
snow alga. Bloom of this
alga causes visible red
snow (watermelon snow).
This species is common in
North America, Japan,
Arctic, Patagonia. The
algae prefer snow surface
rather than ice on
glaciers.
www-es.s.chiba-u.ac.jp/.../snowalgae_ak.html
Low temperature
What happens at low temperature to most organisms?
Microorganisms face a number of biochemical challenges at low
temperatures:
A) Lower rate of biochemical reactions - increse in viscosity and
decline in mobility (for every 10oC drop in temperature, there
is a reduction by a factor of ~2 in the rate of most biochemical
reactions)
B) reduction in membrane lipid fluidity
C) decreased protein flexibility
At even lower temperatures, such as near-freezing or even freezing
temperatures - all macromolecular biosynthesis (DNA, RNA,
proteins, and cell wall) presumably stops.
Freezing of water within a cell is lethal. Exception - nematode
Panagrolaimus davidi, which can withstand freezing of all of
its body water.
Subjecting cells to freezing
Cells cooled too slowly -> the
outside environment freezes
first and extracelluar ice forms
-> creates a chemical potential
difference across the
membrane of cells -> the water
flows outside the cell -> cell
shrinking and dehydration ->
irreveresible damage
Cells cooled too quickly > retains water within the
cell -> the water expands
when frozen -> ice
crystals physically destroy
the cell “intracellular ice
injury”.
http://www.scq.ubc.ca/a-cold-greetingan-introduction-to-cryobiology/
Psychrophiles adaptations
Antifreeze Fish
(Paraliparis Devriesi)
Adaptation: strategies
A. To compensate for the increase in viscosity and decreased mobility
A1. Freezing avoidance - salts and solutes, plus antifreeze cryoprotectant proteins
(glycoproteins) lower the freezing point by 10 to 20oC.
Cryoprotectant proteins are water miscible liquids, they protect the cell from freezing by
reducing the severity of dehydration effects and preventing the formation of ice
crystals within body.
Antarctic fish are able to survive with very small ice crystals present in their body fluids.
A2. Freezing tolerance. Allow the external environment to freeze (extracellular water)->
the change in thermal conductivity insulates the cell against internal freezing (small
number of frogs, turtles, and snake)
B. To compensate for the decreased fluidity in cell membrane - the ratio of the
unsaturated to saturated hydrocarbons must be increased (polyunsaturated fatty acids
in cell membrane)
C. To compensate for decreased protein flexibility - changes in the structure of a cell's
proteins -use enzymes with folds and shapes that promote less rigidity.
Increased expression of heat shock proteins when the temperature is lowered.
To form spores or cysts and try to outlast the cold period (for geologic lengths of time and
become viable again!) Some bacteria survived freezing and thawing without spore
formation.
Heat shock proteins
Sudden decrease in temperature can initiate
specific alteration in gene expression synthesis of heat-shock proteins
Heat shock proteins = molecular chaperones
for proteins - play an important role in
assisting protein folding and the
establishment of proper protein
conformation.
These so-called “heat shock proteins” are not
simply heat proteins. They should more
appropriately be called “temperature and
stress proteins”.
Production of high levels of heat shock
proteins can be triggered by exposure to
different environmental stresses: heat,
cold, inflammation, toxins (metals),
ultraviolet light, starvation, hypoxia
(oxygen deprivation), water deprivation.
http://cryo.naro.affrc.go.jp/index_e/noukenyouranE0721.htm
National Agriculture and Food Research Organization
The structure of the E. coli GroEL heat shock protein. The apical
region is capable of polypeptide binding. The lower region,
(circled, bottom) is concerned with ATP binding.
NASA astrobiologist revives 32,000 year old bacteria
NASA astrobiologist takes ice samples from the permafrost
in Alaska. The samples, dating back some 32,000 years,
contained living organisms. NASA/R. Hoover
Carnobacterium pleistocenium - alive after been thawed from ice dating
back some 32,000 years. Living bacteria are stained green. Image credit:
University of Alabama at Birmingham
Bacteria revived after being frozen 32,000 years ago!
Carnobacterium pleistocenium - found in an ice samples
from the permafrost in Alaska (A layer of soil beneath the
earth's surface that remains frozen throughout the year)
dating back some 32,000 years.
Bacteria had frozen near the end of the Pleistocene Age,
which extended from about 1.8 million years ago to just
11,000 years ago--and earned the new bacterium its
name.
New species of microbe found alive in ancient ice - bacteria
started swimming around on the microscope slide.
Conclusion: microorganisms can be preserved in ice for
geological periods of time!
SEM of carnobacterium pleistocenium,
International Journal of Systematic and
Evolutionary Microbiology (2005), 55, 473
Psychrophiles Eukaryotes - Himalayan midge
Psychrophiles Eukaryotes - Antarctic nematode
The Antarctic nematode Panagrolaimus davidi is the
only animal known to survive extensive
intracellular ice formation.
(Nematode = unsegmented worm-like organisms)
If freezing rate is slow, the nematodes appear not to
freeze. Instead they dehydrate due to the vapour
pressure difference between the supercooled body
fluids within the nematodes and that of the
surrounding ice—a process known as
cryoprotective dehydration.
Nematode Panagrolaimus davidi (A) Frozen
at approximately — 20°C. Bright areas in the
nematode and the background are due to ice
crystals. (C) Just before the disappearance of
the last ice crystals during melting.
Low temperature ecosystems
Diversity of low-temperature ecosystems! From shrimp to whales!
Deep under the Antarctic ice live lots of species of fish, sea stars, jellyfish, shrimp, as well as marine mammals
and penguins, to name a few. Photos Credit: Henry Kaiser, NSF
Psychrophiles - Polyextremophiles - Diatoms
Surirella diatom -in alkaline
and hypersaline Mono Lake.
The large milky turquoise patch visible below
the southern coast of Newfoundland, is a bloom
of phytoplankton.
Diatoms - major group of unicellular eukaryotic algae; one of the most
common types of phytoplankton (microscopic plants found in bodies of
water).
- encased within a cell wall made of silica (hydrated silicon dioxide).
- wide diversity in form, usually consist of two asymmetrical sides with a
split between them, hence the group name.
Environment - wide variety of extreme environments, including ancient
Antarctic Ice, high salt concentrations.
Psychrophiles - Polyextremophiles - Lichens
Lichens - symbiotic associations of a fungus with a
photosynthetic partner that can produce food for the lichen
from sunlight (green alga or cyanobacterium).
• are often the sole vegetation in some extreme
environments - high mountain and at high latitudes;
deserts, frozen soil of the arctic regions.
European Space Agency experiment shows that lichens can
endure extended exposure to space: lichens exposed for 14
days to vacuum, wide fluctuations of temperature, the
complete spectrum of solar UV light and bombarded with
cosmic radiation.
• full rate of survival and an unchanged ability for
photosynthesis!
• Able to recover in full their metabolic activity within 24
hours after extreme dehydration induced by high vacuum.
(Astrobiology. 2007 Jun;7(3):443-54.)
• Experiment extremely important for the possibility of
transfer of life between planets (via meteorites)!
Courtesy ESA.
http://www.esa.int/esaCP/SE
MUJM638FE_index_0.html
Psychrophiles - Polyextremophile - Tardigrades
Tardigrades (water bears) = small, segmented animals;
length 0.1-1.5mm.
Environment: from Himalayas (above 6,000 m), to the deep
sea (below 4,000 m) and from the polar regions to the
equator; in lichens, beaches, soil and marine or
freshwater sediments (up to 25,000 animals per litre).
Tardigrades have been known to survive the following
extremes:
1)Temperature - a few minutes at 151°C; days at minus 200°C.
2)Radiation 100 times higher than lethal dose for humans
3)Pressure very low (vacuum); very high pressures 6,000 atm
4) Dehydration
Adaptation: capable of entering a latent state - cryptobiosis when environmental conditions are unfavorable.
Cryptobiosis = the state of an organism when it shows no
visible signs of life and when its metabolic activity
becomes hardly measurable, or comes reversibly to a
standstill (a unique biological state between life and
death - potentially reversible death). - poorly understood
(read more in Y. Neuman / Progress in Biophysics and
Molecular Biology 92 (2006) 258–267)
High Salinity - Halophiles
Salt flats at Lake Magadi, Kenya. The flats are
red due to the proliferation of halobacteria
An aerial view shows the pink water of Great Salt Lake brushing up against the Ecosculpture "Spiral Jetty" on a salt-crust shore. Image credit: Bonnie Baxter.
Owens Lake. The pink coloration is caused
by halobacteria living in a thin layer of
brine on the surface of the lake bed.
Halophiles -salt-lovers
Halotolerant = are not dependent upon salts in growth media but can tolerate up to 15% salinity.
Extreme halophiles (often known as halobacteria) - unable to survive outside their high-salt native
environment; primary inhabitants of salt lakes, where they tint the water and sediments with bright
colors.
Domains: Archaea, Bacteria, smaller number of Eukarya (yeasts, algae and fungi); Halobacteriacea,
Dunaliella salina
Environment: places where exposure to intense solar radiation leads to evaporation and concentration of
NaCl to near- or even super-saturation; hypersaline bodies of water that exceed the 3.5 % salt of
Earth’s oceans, Great Salt Lake in Utah, The Dead Sea.
High Salinity - halophiles
What happens at high salinity to most organisms?
The greater the difference in salt concentration
between in and outside the cell - the greater
the osmotic pressure (hydrostatic pressure
produced by a solution in a space divided by a
semipermeable membrane due to a differential in
the concentrations of solute).
If we drink salty water we desiccate the cells ->
enzymes and DNA denature or break!
Plants: trigger ionic imbalances -> damage to
sensitive organelles such as chloroplast.
Animals: a high salt concentration within the
cells -> water loss from cells -> brain cells
shrinkage -> altered mental status, seizures,
coma, death.
(Natural salts were used to remove moisture from
the body during mummification).
Adaptation:
Two strategies to cope with osmotic
stress:
1) Maintain high intracellular salt
concentration. Requires extensive
adaptation of the intercellular machinery
(few specialized organisms).
2) Cells maintain low salt concentration
in the cytoplasm, the osmotic pressure
being balanced by:
- producing or taking from the
environment, and accumulating in the
cytoplasm organic molecules (glycerol,
amino acids, sugars).
- selective influx of K+ ions into the
cytoplasm.
High Salinity - Halophiles
Cross section of the
filamentous
cyanobacterium Microleus
embedded in a matrix of a
microbial mat. Solar Lake,
a hypersaline pond in
Egypt.
Cyanobacteria, the first ever oxygenic photosynthesizers, are said to be the source of chloroplasts in
eukaryotes. They are commonly associated with extreme environments
Cyanobacteria - (sometimes called blue-green algae) group of photosynthetic and aquatic
bacteria (not Eukarya!) that contain chlorophyll.
Very important in Earth’s ecological change - the source of the oxygen atmosphere during the
Archaean and Proterozoic Eras; the origin of plants: the chloroplast in plants is assumed to
be coming from symbiosis with a cyanobacterium.
Cyanobacteria can survive in small pockets of water within deposits of salt after water
evaporation.
These type of deposits found on Mars. Jupiter's moon Callisto may have an underground saline
ocean, as well as on the neighboring moon, Europa.
High Salinity - Halophiles
Aphanothece - a blue green alga
in hypersaline environments
Dunaliella - extremely
halophilic green algae; main
food source for brine shrimp.
Great Salt Lake water inoculated on
media plates yields colonies boasting
colorful carotenoids.
Inhabitants of hypersaline lakes experience intense ultraviolet (UV) light.
In order to survive UV, halophiles have efficient DNA repair, but they also have
mechanisms to prevent damage.
Halophilic Archaea have a low number of UV "targets," thymine (one of the four bases in
the nucleic acid of DNA), in their genomes.
Colorful carotenoids – important class of antioxidants that may provide protection from
UV damage -strategy for photoprotection as mutant colorless halophiles are UV
sensitive.
Longevity of Halophiles?
Increasing evidence for the presence of
viable microorganisms in geological
formations that are millions of years
old.
It is not known if ancient salt deposits are
- only a storage area for dormant
microorganisms,
- or they provide a subsurface habitat
in which halophilic microorganisms
can grow and multiply.
The possibility that halophilic microbes
could survive in a state of dormancy
over geological time periods remains
to be proven unequivocally.
Long-term dormancy cannot definitely be
ruled out -> relevant for possible life
on planet Mars, who was hotter and
wetter in the past!
Next lecture
More extremophiles!
High sugar concentration
High pressure
Low pressure
Bacteria that had a trip to the Moon
Alkaline and acid environments
Radiation
Subsurface rocks
oxygen