Extreme Life on Earth

Stephen Eikenberry

13 September 2012

AST 2037

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Life on Earth• So far, we have focused on “normal” life on Earth• The sort of standard critters, plants, and bacteria we are used

to• We will use this as a standard “baseline” for evaluating

conditions for life to develop elsewhere• But …

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The Goldilocks Syndrome• Earth is “just right” for this

sort of life• Conversely, standard life is

“just right” for Earth• Does that mean that life can

ONLY be that way?• Or is it just that, because we

live on Earth, we mostly see “Earth-standard” life?

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“Extreme” Life on Earth• There are forms of life on Earth which seem “extreme”

compared to standard life• (No, not talking about the guys on “Jackass”) • These forms of life show how far life deviates from

“normal” and still survives and reproduces• This gives us some idea of the limitations of life in the

Universe (at least Earth-like life)

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Extreme Life: Aquifex Aeolicus• In the 1960’s, biologists

were interested in studying “how extreme” life could be

• They knew that microbes lived in water downstream from hot springs in Yellowstone National Park

• The springs themselves reached temperatures of ~85C (185 F) – near the boiling point of water

• The question: How far upstream (close to the hottest water) could microbes survive? 5

High Temps: So What?• What’s the Big Deal about life

at high temperatures?• Experience says that putting

living creatures in boiling hot water kills them

• Mmmmm … lobster!• How?• Denaturing of the proteins• High heat causes proteins

to lose some of their structural/chemical properties

• Breaks down the structure of the living cells

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Aquifex Aeolicus Surprise• Biologists discovered

bacteria in the hottest parts of the hot springs themselves

• These creatures survive – even thrive and reproduce!! – at ~85C (185 F), near the boiling point of water

• Picture shows microbial mats (as in stromatolites) in Yellowstone hot spring

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Aquifex Aeolicus Properties• These are very small bacteria• Prokaryotes• Genome structure is only 1/3 as long (complex) as E. coli (a

model “simple” bacteria)• Single DNA molecule in a circular chromosome

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Aquifex Aeolicus Metabolism• A. aeolicus survives from H,

O, CO2, and mineral salts• Requires oxygen for

respiration (so, not that primitive)

• But … no need for sunlight, nor sunlight-using food !!

• Purely chemical food source (in the presence of thermal energy from the water)

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The colors of Prismatic Spring in Yellowstone come primarily from the hyperthermophile microbes in it

Archaea• Genetic diversity studies show

that A. aeolicus is one of the most “divergent” bacteria known

• I.e. it has little in common with many of the other bacteria

• This and others led to the re-classification of 3 “Domains” of life on the basis of genetic linkage: • Archea• Bacteria• Eukaryota

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Archaea• Very small critters (~1 micron in length)• No nucleus (like bacteria)• Different tRNA from bacteria and Eukaryotes (which have

same tRNA as each other)• Cell structure LOOKS like other cells, but made from

different chemicals• All bacteria/eukaryotes us D-glycerol isomers; Archaea only

use L-glycerol

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Archaea & Extremophiles• Archaea are typically “primitive” organisms• Most single-celled “extremophiles” are members of archaea

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Chemosynthesis• Energy generation NOT dependent on sunlight• Often (but NOT always) does not depend on other critters• A. aeolicus survives by pure chemosynthesis (no

photosynthesis; no eating other life forms)• Types of chemosynthetic life:• Methanogens• Halophiles• Sulfur reducers• Thermoacidophile (i.e. Aquifex aeolicus)

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Methanogens• Things that use chemosynthesis to survive, and produce

methane (CH4) as a by-product• Well-known examples:• Swamp gas bubbles (methanogen byproduct)• Flatulence (bovine, human) – mmmm … Tijuana Flats!

• Methanogens typically only thrive (and only survive for long) in environments where other “chemically aggressive” elements (like O) are rare

• Methanogens have been found thriving as slime mats on deep rocks below Earth’s surface (endoliths)

• Also found in extreme cold/dry desert environments

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Halophiles• Microbes that survive by

chemosynthesis in VERY salty water (i.e. 5x to 10x that of ocean water)

• Locations:• Great Salt Lake (Utah)• Dead Sea (Israel/Jordan)• Owens Lake (California)• Evaporation estuaries in

San Francisco Bay

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Black Smokers• Black smoker vents• Found in deepest parts of the

ocean• Volcanic, mineral-enriched

water outflows• Rich in iron, sulfur

compounds• Very little/no oxygen• Discovered in the 1970s• Temps as high as 750 F (!!)• Does not boil, though, due to

extreme pressure at this depth

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Black Smoker Structure

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Black Smoker Ecology• Deep sea exploration vehicles investigate black smokers in

the 1980’s• Much to everyone’s surprise, they find LIFE !!

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Black Smoker Ecology• Not just life – fully-developed ecosystems!• Crabs, shrimp, clams, Pompeii worms

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Pompeii Worms• Tube worms anchored near black smoker vents• Bottom end has very high temps; top end more like 70F• Hot water flows through tubes; length as much as 10 feet!

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Pompeii Worms• “Hairy” back is heat-resistant microbe mat (symbiotic with

worm mucus)• Red “feathers” include hemoglobin; separates hydrogen

sulfide from vent flow

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What feeds the ecosystem?• Sulfur-reducing extremophile archaea!• Metabolism centers on hydrogen sulfide (not oxygen, nor

CO2!)• Pompeii worms (and some clams) seem to have symbiotic

relationship with microbes• Worm “feathers” gather H2S and bring it into tube, where

billions of microbes live• Microbes “digest” minerals with sulfur metabolism, releasing

CO2 byproduct• Worm uses CO2 to digest minerals as well• Other life forms live on microbes, worms, etc.• Worms may live as long as 200+ years (!)

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Summary• Life is weird• Extremophiles are found everywhere from petroleum

reservoirs to the Dead Sea to hot springs to deep sea vents• Most single-celled extremophiles are Archaea• Genetically distinct from eukaryota and bacteria• tRNA differences and chemical differences too

• Metabolism may be oxygen-independent (even oxygen-phobic!)

• Black smoker ecosystems show tremendous diversity, with basis in (and symbiotic relationships with) sulfur-reducing Archaea

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