PTYS 214 – Spring2011

Homework #7 DUE in class TODAY

Homework #8 available for download on the class websiteDUE Tuesday, Apr. 5

Class website: http://www.lpl.arizona.edu/undergrad/classes/spring2011/Pierazzo_214/

Useful Reading: class website “Reading Material” http://en.wikipedia.org/wiki/Extremophile http://serc.carleton.edu/microbelife/extreme/about.html

Announcements

Quiz #6

Total Students: 23

Class Average: 2.6

Low: 0.5

High: 4

Quizzes are worth 20% of the grade

Extreme Environments

Physical extremes: - Temperature - Pressure - Radiation

Geochemical extremes: - pH (acidity levels) - Salinity - Desiccation - Oxygen species - Redox potential

For any particular property (T, pH, salinity) extreme values are values far from the typical range for human life

Extremophiles

Organisms (mostly microbes) that thrive in (and sometime require) extreme conditions

The earliest living organisms on Earth were extremophiles

Early-Earth environment:– Atmosphere without oxygen:

no UV protection– Oceans were hot and probably acidic (volcanism)

Importance of Temperature

Organisms have upper temperature limits - chlorophyll, proteins and nucleic acid denature at high temperatures

Enzymes have optimal temperatures for activity - they slow down at low temperatures

Solubility of gases goes down as temperature goes up

At low temperature water freezes; crystals then break up membranes etc. (but the expansion of water to ice means layers of ice ‘insulate’ water below… for most liquids lakes would freeze from bottom up)

ThermophilesHigh Temperature Lovers

Reproduce and grow readily in temperatures higher than 45°C (geothermal sites)

Hyperthermophilic Optimum growth at >80°C (hydrothermal

vents)

Current upper limit foractive growth is 121°C - Pyrolobus fumarii -

1 μm

1 μm

Example: Octopus Spring, Yellowstone Nat. Park(pH: 8.3-8.8)

Rotschild & Mancinelli (2001) Life in extreme environments. Nature 409, 1092

Synechococcus

Thermocrinis ruber

Chloroflexus and others

Planet Earth Video

Psychrophiles or CryophilesLow Temperature Lovers

Obligatory psycrophilic (“cold loving”) No growth at >15°C (polar sediments, sea ice)

Psychrophilic Optimum growth at <20°C (polar sediments, sea

ice)

Current lower limit for active growth is -20°C (water with high salt content can be liquid even at -30°C)

Grylloblatids, or ice bugs, have body fluids that act as antifreeze

Snow algae (red snow or watermelon snow) are cold-tolerant algae and cyanobacteria that grow on snow and ice during alpine and polar summers

Liq

uid

wat

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sa

lts

High Pressure High pressure can make the cell membranes relatively

impermeable for nutrients

Piezophilic (or barophilic) Optimum growth at >>1 atm some growth at 1

atm

Obligatory piezophilic Cannot survive at low pressures

Current upper limit is >1000 atm - Halomonas salaria – an obligatory piezophile

(at the bottom of the Marianas Trench, 10,898 m, pressure is ~800 atm)

High-Low Acidity (pH)

pH = -log10[H+]

Amount of H+, it measures the acidity of a solution

Within the cell pH levels must be neutral (proteins denature at very low pH)

Acidophile Optimal growth at pH < 2 - 3

Alkaliphile Optimal growth at pH > 9 - 10

pH limits

Current limits: pH ~0 Ferroplasma acidarnamus (acid mine drainage, Iron Mountain, CA)

pH = 13 Plectonema (soda lakes)

Tinto river (Andalusia, Spain)

With a pH of about 2 (causing Fe to be soluble in water), it has gained scientific interest due to the presence of extremophile aerobic bacteria that dwell in the water

Salinity Prevents protein aggregation: proteins are less soluble

at high salt concentrations

Halophilic Optimum growth at seawater salinity (~3%)

Extremely halophilic Optimum growth in solutions with > 10-15%

salt

Dunaliella salina a halophilic pink micro-algae especially found in sea salt fields, can

survive in saturated salt water

Water availability

Extreme desiccation can cause irreversible phase changes to lipids, proteins and nucleic acids

Xerophiles grow in environments with low water availability (low “water activity” aw<0.8)

− aw(distilled water) = 1− aw(saturated NaCl) = 0.75− aw(honey or indoor air) = 0.5 - 0.7

Mold and yeast can survive at aw = 0.6

Tardigrades – “water bears”

No larger than about 1 mm, they have short, plump bodies

In anhydrobiosis (their body desiccates and waits for moisture to return) they can survive: -272.95°C (0.05K) for 20 Hours -200°C for 20 Months +120°C (above boiling) Pressures of 1,000 atm Pure vacuum Live over 125 years

Endoliths Anaerobic organisms that live in the pores between

mineral grains of a rock and can survive by feeding on Fe, K, or S (they can “eat” rock)

Found in rocks as deep as 3 km, where both temperature and pressure are quite high

Bacillus infernus is an endolitic hyperthermophile found up to 3 km beneath the Earth's surface

Photo courtesy of US Dept. Energy

Example: Beacon sandstone, McMurdo Dry Valleys, Antarctica

PolyextremophilesOrganisms that combine several extremophilic features

(most extremophiles are really polyextremophiles)

Blue bands are layers of cryptoendolithic lichen communities (algae, fungi and

bacteria)

One of the most radiation-resistant organisms known, it can survive cold, dehydration, vacuum, and acid

Polyextremophiles:Deinococcus Radiodurans(a.k.a.“Conan the bacterium”)

Radiation-resistant: it can stand around 1,000 time radiation amounts that would kill humans!

It carries between 4 and 10 copies of its DNA, making it easy to repair damage from radiation, or dehydration

Arsenic-based Life?

http://www.youtube.com/watch?v=SxEvOCIROGo

Activity

Extreme Environments and the Life that Lives there

Bacteria A Environment X: too cold + no chemical energy + no org. CEnvironment Y: too hot + no organic C + no salinity

(survives even if light decreased nearly to zero)

Bacteria B Environment Y: no oxygen + too hot + low salinityEnvironment Z: no oxygen + no inorganic C

(it appears as it needs light to survive)

Bacteria C Environment X: no chemical energy + too cold + high salin.Environment Z: no inorganic C + high salinity

(survives even if light decreased nearly to zero)

Environment Z

Environment X

Environment Y

Activity: Extremophiles

Looking for “strange life” on Earth…

Any new hydrothermal vent contain new life forms

deep sub-seafloor biosphere is the least explored habitat on Earth, yet it may make up 1/10 to 1/3 of Earth’s living biomass!

Lots of new life forms await our discovery…

…may teach us to look for “strange life” beyond Earth!

Mars may have regions in its deep subsurface permafrost that could harbor endolith communities

On Europa, the subsurface water ocean may harbor life, especially at the hypothesized hydrothermal vents at the ocean floor.

Venus’ stable cloud layers, 50 km above the surface, have hospitable climates and chemical disequilibrium, fueling speculations that microbes could live there

On Titan, data from Cassini/Huygens suggest a near-surface chemistry consistent with the hypothesis that organisms may be consuming hydrogen, acetylene and ethane, to produce methane (but this is not proof)

Earth’s ‘Extreme’ is ‘Normal’ Somewhere Else…