Extreme Life on Earth Stephen Eikenberry 13 September 2012 AST 2037 1
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 2
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 t d life? 3
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) 4
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? 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 6
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 7
Aquifex Aeolicus Properties These are very small bacteria Prokaryotes Genome structure re is only 1/3 as long (complex) as E. coli li(a model simple bacteria) Single DNA molecule in a circular chromosome 8
Aquifex Aeolicus Metabolism A. aeolicus survives from H, O, CO 2, and mineral salts Requires oxygen for respiration (so, not that primitive) But no need dfor 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 9
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 reclassification of 3 Domains of life on the basis of genetic linkage: Archea Bacteria Eukaryota 10
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 11
Archaea & Extremophiles Archaea are typically primitive organisms Most single-celled extremophiles are members of archaea 12
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) 13
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 14
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 Halophiles 15
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 Black Smokers 16
Black Smoker Structure 17
Black Smoker Ecology Deep sea exploration vehicles investigate black smokers in the 1980 s Much to everyone s surprise, they find LIFE!! 18
Black Smoker Ecology Not just life fully-developed ecosystems! Crabs, shrimp, clams, Pompeii worms 19
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! 20
Pompeii Worms Hairy back is heat-resistant microbe mat (symbiotic with worm mucus) Red feathers include hemoglobin; separates hydrogen sulfide from vent flow 21
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 H 2 S and bring iti 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 (!) 22
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 oxygenphobic!) Black smoker ecosystems show tremendous diversity, with basis in (and symbiotic relationships with) sulfur-reducing Archaea 23