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
• 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".
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.
Protozoa = one-celled eukaryotes.
Complex organisms (Eukarya) occupy a more restrictive thermal range than Bacteria and Archaea
Low temperature - Psychrophiles
Psychrophiles - extremophiles capable of growth and reproduction at or below 15oC.
Environments ubiquitous on Earth - alpine and arctic soils (permafrost), high-latitude and deep oceanwaters, arctic ice, glaciers, snowfields, & refrigerated appliances.
1) Obligate psychrophiles - have optimum growth temperature of 15°C or lower and cannot grow in aclimate 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 thanobligate 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.
Subglacial stream - Glacier du Mont Mine, Swiss Alps.
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 brineinclusions. Water can remain liquid at temperatures lowerthan -30oC in the presence of salts and other solutes.
Many species of snow algae were observed on Alaskanglaciers (green algae and cyanobacteria).
Some of them produce brilliant colored spores. They alter thealbedo of the snow and induce snowmrlt, incresing theavailability of liquid water.
Some organisms produce extra-cellular enzymes that lead topitting 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 thesun)
www-es.s.chiba-u.ac.jp/.../snowalgae_ak.html
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.
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.
http://www.scq.ubc.ca/a-cold-greeting-
an-introduction-to-cryobiology/
Cells cooled too quickly -
> retains water within the
cell -> the water expands
when frozen -> ice
crystals physically destroy
the cell “intracellular ice
injury”.
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
Subjecting cells to freezing
Psychrophiles adaptations
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 byreducing the severity of dehydration effects and preventing the formation of icecrystals 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 (smallnumber of frogs, turtles, and snake)
B. To compensate for the decreased fluidity in cell membrane - the ratio of theunsaturated to saturated hydrocarbons must be increased (polyunsaturated fatty acidsin cell membrane)
C. To compensate for decreased protein flexibility - changes in the structure of a cell'sproteins -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 andbecome viable again!) Some bacteria survived freezing and thawing without sporeformation.
Antifreeze Fish(Paraliparis Devriesi)
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
Bacteria revived after being frozen 32,000 years ago!
Carnobacterium pleistocenium - found in an ice samplesfrom the permafrost in Alaska (A layer of soil beneath theearth'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 just11,000 years ago--and earned the new bacterium itsname.
New species of microbe found alive in ancient ice - bacteriastarted swimming around on the microscope slide.
Conclusion: microorganisms can be preserved in ice forgeological periods of time!
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
NASA astrobiologist takes ice samples from the permafrost
in Alaska. The samples, dating back some 32,000 years,
contained living organisms. NASA/R. Hoover
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
Diatoms - major group of unicellular eukaryotic algae; one of the mostcommon types of phytoplankton (microscopic plants found in bodies ofwater).
- encased within a cell wall made of silica (hydrated silicon dioxide).
- wide diversity in form, usually consist of two asymmetrical sides with asplit between them, hence the group name.
Environment - wide variety of extreme environments, including ancientAntarctic Ice, high salt concentrations.
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.
Psychrophiles - Polyextremophiles - Lichens
Lichens - symbiotic associations of a fungus with aphotosynthetic partner that can produce food for the lichenfrom sunlight (green alga or cyanobacterium).
• are often the sole vegetation in some extremeenvironments - high mountain and at high latitudes;deserts, frozen soil of the arctic regions.
European Space Agency experiment shows that lichens canendure extended exposure to space: lichens exposed for 14days to vacuum, wide fluctuations of temperature, thecomplete spectrum of solar UV light and bombarded withcosmic radiation.
• full rate of survival and an unchanged ability forphotosynthesis!
• Able to recover in full their metabolic activity within 24hours after extreme dehydration induced by high vacuum.(Astrobiology. 2007 Jun;7(3):443-54.)
• Experiment extremely important for the possibility oftransfer 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 deepsea (below 4,000 m) and from the polar regions to theequator; in lichens, beaches, soil and marine or freshwatersediments (up to 25,000 animals per litre).
Tardigrades have been known to survive the followingextremes:
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 novisible signs of life and when its metabolic activitybecomes hardly measurable, or comes reversibly to astandstill (a unique biological state between life anddeath - potentially reversible death). - poorly understood
(read more in Y. Neuman / Progress in Biophysics andMolecular Biology 92 (2006) 258–267)
High Salinity - Halophiles
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.
An aerial view shows the pink water of Great Salt Lake brushing up against the Eco-
sculpture "Spiral Jetty" on a salt-crust shore. Image credit: Bonnie Baxter.
Salt flats at Lake Magadi, Kenya. The flats are
red due to the proliferation of halobacteriaOwens Lake. The pink coloration is caused
by halobacteria living in a thin layer of
brine on the surface of the lake bed.
High Salinity - halophiles
What happens at high salinity to most organisms?
The greater the difference in salt concentrationbetween in and outside the cell - the greaterthe osmotic pressure (hydrostatic pressureproduced by a solution in a space divided by asemipermeable membrane due to a differential inthe concentrations of solute).
If we drink salty water we desiccate the cells ->enzymes and DNA denature or break!
Plants: trigger ionic imbalances -> damage tosensitive organelles such as chloroplast.
Animals: a high salt concentration within the cells-> water loss from cells -> brain cellsshrinkage -> altered mental status, seizures,coma, death.
(Natural salts were used to remove moisture fromthe 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
Cyanobacteria - (sometimes called blue-green algae) group of photosynthetic and aquaticbacteria (not Eukarya!) that contain chlorophyll.
Very important in Earth’s ecological change - the source of the oxygen atmosphere during theArchaean and Proterozoic Eras; the origin of plants: the chloroplast in plants is assumed tobe coming from symbiosis with a cyanobacterium.
Cyanobacteria can survive in small pockets of water within deposits of salt after waterevaporation.
These type of deposits found on Mars. Jupiter's moon Callisto may have an underground salineocean, as well as on the neighboring moon, Europa.
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
High Salinity - Halophiles
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.
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.
Longevity of Halophiles?
Increasing evidence for the presence ofviable microorganisms in geologicalformations that are millions of yearsold.
It is not known if ancient salt deposits are
- only a storage area for dormantmicroorganisms,
- or they provide a subsurface habitatin which halophilic microorganismscan grow and multiply.
The possibility that halophilic microbescould survive in a state of dormancyover geological time periods remainsto be proven unequivocally.
Long-term dormancy cannot definitely beruled out -> relevant for possible lifeon planet Mars, who was hotter andwetter 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
