28 January 2016

• Extreme Conditions
• Tree of Life

• Conditions on early earth may have been
“ extreme ” compared to present-day
• Extremophiles - organisms that thrive in exteme environments
– Heat/Cold
– Acids/alkalines
– High pressures
– dessication

Extreme Conditions
• Majority of organisms on Earth thrive in the temperature range 20-45 ° C
(mesophiles)
• Usual response to extreme temperatures:
– Cold:
• Formation of ice crystals in the body
– Hot:
• Structural breakdown of biological molecules
(proteins and nucleic acids)
• Disruption of cells ’ structural integrity due to increased membrane fluidity

Extreme Conditions

Extreme Conditions
• Thermophiles live between 50 and 80 ° C
–Example: Thermoplasma
•Archaea
•Lives in volcanic hot springs
• Hyperthermophiles live between 80 and 115 ° C
–Example: Sulfolobus
•No multicellular plants or animals can tolerate >50
° C
•No microbial eukarya can tolerate >60 ° C

Extreme Conditions
• First true thermophile discovered in
Yellowstone National
Park in 1960s
• > 50 hyperthermophiles have been isolated to date
– Many live in or near deep-sea hydrothermal systems
(black smokers)

Extreme Conditions
• Since high temperatures change membrane fluidity, adaptation is change of membrane composition
• Evolution of proteins to better cope w/ high temps

Extreme Conditions
• Supported in frozen environments of Earth
• Lowest recorded temperature for active microbial communities: -18 ° C
• Found in all 3 domains of life

Extreme Conditions
• Low temps mean decrease in membrane fluidity, so adaptation is adjustment of ratios of lipids in their membranes
• Prevent water from freezing with soluble compounds that lower freezing temp of water (e.g. thermal hysteresis proteins)

• UV and ionizing radiation can do serious damage to
DNA
– Deinococcus
radiodurans can withstand high-dose radiation because it can accurately rebuild its DNA
– Also able to cope with extreme dessication, so also a xerophile - thus known as a polyextremophile
Extreme Conditions

Extreme Conditions
• Most biological processes occur in middle of pH scale (4-8)
• Acidophile - thrive at 0.7-4
– Occur in geochemical activities
• Sulfur production at hot springs and deep-sea vents
– Cope by keeping acid OUT. Evolved enzymes on the front lines that tolerate extreme acidity
• Alkaliphile - thrive at 8-12.5
– Live in soils containing carbonate and soda lakes
– Above pH of 8, RNA breaks down, so alkaliphiles maintain neutrality inside cells

Extreme Conditions
• Acidophile - thrive at 0.7-4
– Occur in geochemical activities
• Sulfur production at hot springs and deep-sea vents
– Cope by pumping H+ out of cells at a high rate
• Alkaliphile - thrive at 8-12.5
– Live in soils containing carbonate and soda lakes
– Above pH of 8, RNA breaks down, so alkaliphiles maintain neutrality inside cells
Acidic mudpot : located in
Yellowstone NP, home of
Sulfolobus acidocaldarius.
Photo courtesy of National Park
Service

Extreme Conditions
• Halophiles require high concentrations of salt to live (2-5 times that in seawater)
• Found in Great Salt Lake,
Dead Sea, salterns
• Can be coincident with high alkalinity environments
• Survive by producing large amounts of internal solute so as to not lose water via osmosis
Great Salt Lake, UT.
Carotenoids seen here are biproduct of halophiles. Photo
Courtesy of just_javier on Flickr

Extreme Conditions
• Some organisms survive low-water environments via anhydrobiosis, a state of suspended animation

Extreme Conditions
• Undersea pressures are much greater than surface pressures
– Boiling point increases with pressure, so liquid water at ocean floor could be 400 ºC
– Pressure compresses volume, so peizophiles have increased membrane fluidity so they don ’ t get “ smushed ”
• Upper atmosphere pressures are much lower than surface pressures

Extreme Conditions
• Aerobic metabolism is more efficient than anaerobic, but it kills cells quicker via oxidation
• Many organisms with aerobic metabolisms combat oxidation with natural anti-oxidants

Other Worlds
• Hotsprings
• The deep sea
• Hypersaline environments
• Evaporites
• The atmosphere
• Ice, permafrost, snow
• Subsurface environments

• “Prokaryotic”:
– Smaller.
– (Often) no nucleus.
– Single-celled organisms.
• Eukaryotic:
– Larger.
– More complex.
– Membraneenclosed nucleus with
DNA.
– Organisms can be single-celled or multi-cellular.

• Bacteria:
– Most prokaryotes (“germs”) you are aware of (E. coli,
Salmonella, …).
• Archaea:
– “Ancient” (?), not really, it’s all relative.
– Extreme environments.

• Amoebae, plants, fungi,animals, you!

• Evolutionary branches determined by DNA comparisons.
• Bacteria seem most ancient; archaea closer to eukarya.

• Macroscopic life diversity “exploded” ~540 Myr ago:
– Oxygen levels had risen: A good energy source!
– But O
2 attacks organic bonds: many microbes went extinct!
– Soon after several Snowball Earths: coincidence or trigger?
Cambrian sea Trilobite fossil

• Burgess Shale,
British Columbia.
Hallucigenia

• For macroscopic life, protective ozone (O
3
) layer was vital step to inhabiting land:
– Shields the surface from dangerous ultraviolet sunlight.
• Life generated O
2
(through photosynthesis), which forms O
3
, which protects life!

Eons:
Hadean:
“hellish”
Archaean:
“ancient”
Proterozoic: “earlier life”
Phanerozoic: “visible life”
Eras:
Paleozoic:
“old life”
Mesozoic:
“middle life”
Cenozoic: “recent life”

1.
“Organic soup” vs. dilute solution.
2.
Complex organics developed (mineral templates?).
3.
“Pre-cells” enclosed complex organics.
4.
Natural selection increased RNA complexity.
5.
DNA developed within some successful cell(s).
A reasonable scenario, though many details are missing!

Other Worlds
• If we ’ ve seen life thrive in extreme circumstances on Earth, why not on other planets?
• Mars holds most promise
• What about moons in our solar system:
– Europa
– Titan
– Enceladus

• Life exists w/o photosynthesis in the deep ocean
• Europa has a subsurface ocean
• Life may exist beneath the surface
Other Worlds

Other Worlds
• Airborne micro-organisms?
• Extremes to withstand:
– Dessication
– Radiation

Other Worlds
• Host to several extreme environments
– Deserts
– Ice, permafrost, snow
– Subsurface

Other Worlds
• Microbes and algae exist in frozen environments on
Earth
• Maybe not thriving, but microbial survivors could exist

Other Worlds
• Best chance of withstanding
Martian extremes
– No liquid water at surface
– Low pressure
– CO
2
-rich atmosphere
– Only 43% solar radiation at
Earth
• Subsurface provides
– Protection
– Possible liquid water
– Energy source for chemolithoautotrophs

• Earth life arose more than 3.5 billion years ago. Our oldest ancestors may have been extremophiles
• Life has become progressively larger and more complicated, but large organisms are recent: 650 million years
• Extremophiles live at high and low T, P, pH; high salinity and radiation
• Earth’s extreme environments resemble other planets