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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” 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 ~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 6 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 7 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 8 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 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 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 15 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 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 70F • 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 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 (!) 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