Phys 214. Planets and Life

Dr. Cristina Buzea

Department of Physics

Room 259

E-mail: cristi@physics.queensu.ca

(Please use PHYS214 in e-mail subject)

Lecture 18. Life at the extremes. Part I.

February 25th, 2008

Contents

• Textbook pages 178-181

• & the latest research in the field

• Life at the extreme. Part I.

• Temperature extremes - High temperature

Life at the extreme

• 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 itcompared 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

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 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)

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

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 (YellowstoneNational Park), and deep sea hydrothermal vents.

1) Obligate thermophiles (extreme thermophiles) require very high temperatures forgrowth

2) Facultative thermophiles (moderate thermophiles) can thrive at high temperaturesbut also at lower temperatures (below 50 °C).

3) Hyperthermophiles are particularly extreme thermophiles for which the optimaltemperatures are above 80 °C.

Yellowstone National Park, Geothermal area in El Tatio Chile, Deep sea hydrothermal vents

Hyperthermophiles

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).

Hydrothermal vents Yellowstone National Park hot spring. Orange

and brown microbial mats of hyperthermophilic

bacteria and archaea.

Red coloration on rocks near Naples,

Italy, produced by the hyperthermophile

Sulfolobus solfataricus.

Hyperthermophiles

Discovered in the 1960s, in hot springs in Yellowstone National Park. Since then, more thanfifty species have been discovered.

Domain: Archaea (majority), Bacteria (some cyanobacteria and anaerobic photosyntheticbacteria 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 interestbecause of its ancient genetic make-up -may have been among the earliest organisms onEarth!)

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 hasbeen able to double its population during 24 hours in an autoclave at 121°C (hence itsname). (An autoclave is a pressurized device designed to heat aqueous solutions above theirboiling point to achieve sterilization.)

• The ability to grow at 121 degrees Celsius is significant because medical equipment isexposed to this temperature for sterilisation in an autoclave. Prior to the 2003 discoveryof Strain 121, a fifteen-minute exposure to autoclave temperatures was believed to killall living organisms.

• The upper temperature for life is still to be determined! There is evidence of intactmicroorganisms with DNA and RNA in hydrothermal vent sulfides at temperaturesexceeding 200oC.

Hyperthermophiles

• 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.

Beppu hot spring, Japan.

Phylogenetic tree

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 orwith increasing salt concentration.

A1. Some organisms ingest or produce salts (KCl, MgCl2) which enhance the stability of theDNA chain by partially canceling out the negative charges of the phosphate groups inthe 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 (andtherefore function) at high temperatures. Such proteins have evolved to exhibit optimalfunction at much greater temperatures.

heat stable proteins - proteins resistant to unfolding - more densely packed to excludeinternal water, and more hydrophobic, have more salt bridges, with more bonds betweenpolypeptide chains to provide sturdiness. (The enzyme amylopullunase does notdenature 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 increasedmobility and fluidity at high temperatures.

Hydrothermal vents

• Hydrothermal vents are underwater oases, providing habitat formany 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 spreadingapart and magma is coming up from below to form mid-oceanridges.

• As cracks form at these spreading centers, seawater seeps a mile ortwo down into the hot rock.

• Enriched with minerals leached from the rock, the water heats andrises to the ocean floor to form a vent.

• Water pouring out of vents can reach temperatures up to about4000C; the high pressure keeps the water from boiling.

• However, the intense heat is limited to a small area. Largetemperature gradient - within less than an inch of the vent opening,the water temperature drops to 2 C, the ambient temperature ofdeep seawater.

• Most of the creatures that congregate around vents live attemperatures just above freezing. Thus chemicals are the key tovent life, not heat!

• harsh combination of toxic chemicals, high temperatures, highpressures, and total darkness at these vents.

Hydrothermal vents

• The most hardy hyperthermophiles yet discovered live on the superheated walls of deep-

sea 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.

Pink jellyfish from (Stauromedusae) and spiky tubeworm near the newly

discovered Medusa hydrothermal vent field. NSF Tube worms.

Hydrothermal vents

• Mussels, shrimp, clams, and crabs are abundant at many vents, but these are not thesame species that you find in seafood dishes.

• The cocktail-size shrimp that dominate vents in the mid-Atlantic, for example, have noeyes. However, at least one species has an extremely sensitive receptor on its head thatmay 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 chemical-loaded seawater that would kill ordinary shellfish.

• The most prevalent chemical dissolved in vent water is hydrogen sulfide, which smellslike rotten eggs. This chemical is produced when seawater reacts with sulfate in therocks below the ocean floor. Vent bacteria use hydrogen sulfide as their energy sourceinstead of sunlight. The bacteria in turn sustain larger organisms in the vent community.

Snails, fish, crabs living near deep sea vents.

http://www.soest.hawaii.edu/expeditions/mariana/dailyupdates-39.htm

Chemosynthetic Bacteria

Hydrothermal vents

• 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.

Iwa hirsute, the Yeti crab - blind

creature has the vestige of a

membrane instead of eyes.

Brisingid sea stars in the Lau Basin Tube worms

High temperature -large organisms

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 sticksout of the tubes into water that is a much cooler 22º F.

Chemolithotrophic Bacteria form a "fleece-like" covering on their backs - living in asymbiotic relationship, the worms secrete mucous from tiny glands on their backs tofeed the bacteria, and in return they are protected by some degree of insulation.

Pompeii Worm, Alvinella pompejana

Next lecture

Extremophiles part II.

Quiz. 10 minutes