1. Stephen Eikenberry 13 September 2012 AST 2037
Extreme Life on Earth
Stephen Eikenberry
13 September 2012
AST 2037

2. 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 …

3. 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?

4. “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)

5. 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 ~85C (185 F) – near the boiling point of water
The question: How far upstream (close to the hottest water) could microbes survive?

6. 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

7. Aquifex Aeolicus Surprise
Biologists discovered bacteria in the hottest parts of the hot springs themselves
These creatures survive – even thrive and reproduce!! – at ~85C (185 F), near the boiling point of water
Picture shows microbial mats (as in stromatolites) in Yellowstone hot spring

8. 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

9. 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)
The colors of Prismatic Spring in Yellowstone come primarily from the hyperthermophile microbes in it

10. 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

11. 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

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

13. 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)

14. 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

15. 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

16. 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

17. Black Smoker Structure

18. Black Smoker Ecology
Deep sea exploration vehicles investigate black smokers in the 1980’s
Much to everyone’s surprise, they find LIFE !!

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

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

21. Pompeii Worms
“Hairy” back is heat-resistant microbe mat (symbiotic with worm mucus)
Red “feathers” include hemoglobin; separates hydrogen sulfide from vent flow

22. 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 (!)

23. 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