41 st Saas‐Fee course from Planets to Life 3‐9 April 2011 Lecture 2: The “top down” approach to understanding the origin of life – cont. • Understanding the characterisFcs of the organisms close to the root of the tree – Most are extremophiles (grow at high temperatures, high and low pH, high salt, etc) – The origin of metabolism – The “RNA” world – The possible role of viruses in the origin of life – The possible importance of “biofilms” in the early evoluFon of life
CharacterisFc differences between the three domains of life: Archaea, Bacteria and Eukarya Characteristics* Archaea Bacteria Eukarya Cells with membrane-bound No No Yes nucleus and other organelles DNA circular 1 Yes Yes No Ribosome size 70S 70S 80S Membrane lipids Ether linked Ester linked Ester linked No PDG 2 Cell walls PDG No Histone proteins Yes No Yes Operons in DNA Yes Yes No Ribosome structure distinct distinct Archaeal-like Antibiotic sensitivity No Yes No Photosynthesis No Yes Yes Growth at temperatures >80°C Yes Yes No *There are many physiological characterisFcs that are found only in bacteria and archaea. 1 There are some excepFons. 2 PDG is pepFdoglycan; Archaea do not have PDG but do have at least 7 different cell surface layers (protein, lipid, etc)
The endoplasmic reFculum is an interconnected network of tubules, vesicles and is involved in the synthesis of proteins, lipidss, sugar metabolism, etc Longitudinal secFon through the flagella area The kinetosome (basil body) that is the anchoring site for a flagellum
Limits of Life and Limits of Diversity • Are their limits to evolutionary diversity of life as we know it? • What environmental conditions limit where life can exist? What did Darwin have to say that is germane to these questions?
Quotes from The Origin of Species In reference to natural selec.on : “I can see no limit to this power, in slowly and beautifully adapting each form to the most complex relations of life” Darwin’s ending paragraph : “…from so Darwin's most famous book, was simple a beginning endless published in 1859. Within 20 years it forms most beautiful and convinced most of the internaFonal most wonderful have been, scienFfic community that evoluFon and are being evolved” was a fact.
“I can see no limit to this power etc” The blobfish ( Psychrolutes marcidus ) is found at depths greater than 5000 m off the coast of Australia and Tasmania. To remain This crustacean invades a fishes buoyant, the flesh of the blobfish is a mouth, devours its tongue, and takes gelaFnous mass with a density slightly less the tongues place. It then acts like a than water. This allows the fish to float above tongue; the fish can use it to grip and the sea floor without expending energy on swallow prey ‐ the parasite gets first swimming. The relaFve lack of muscle is not dibs at the food. (From: Carl a disadvantage as it primarily swallows edible Zimmer, Parasite Rex, Simon & macer that floats by in front it (adult blobfish Schuster) ~30 cm long).
“there are no limits” ‐ The water bear (Tardigrade) could easily survive on Mars and in the ice of Europa TarFgrades are between 0.05 and 1.2 mm in length, have feet with claws like bears and walk like bears. They are found everywhere including hot springs, in a 5m layer of solid ice, on the top of the Himalayas, stone walls etc but mostly live in moss. They could survive on Mars because:
The water bear is capable of surviving for more than 12 years in a completely dry state called the “tun” state or in “cysts”. In the “tun”state they will survive in liquid helium, absolute alcohol or even ether and brine. Just add water and they come back to life ‐ just like instant coffee “gummy bear” Dry form “tun” Asphyi.c state ‐O 2 coming back to life with addi.on of water
41 st Saas‐Fee course from Planets to Life 3‐9 April 2011 The “top down” approach to understanding the origin of life • Understanding the characterisFcs of the organisms close to the root of the tree – Most are extremophiles (grow at high temperatures, high and low pH, high salt, etc)
The Universal PhylogeneFc Tree: Origin of Life and EvoluFon ImplicaFons What does this tree tell us about the Universal Phylogenetic Tree evolu8on of organisms? 1. There are three domains of life 2. All extant life arose from a common ancestor 3. Bacteria and Archaea thought to be part of the same group of organisms (prokaryotes, Monera etc) are disFnctly different 7. The Eukarya evolved from the archaea 8. The deepest rooted organisms are thermophiles (hyperthermophiles) 11. The proFsts are polyphyleFc (see diplomonads and ciliates) 12. The cyanobacteria (the mother of all oxygen producing photosyntheFc oganisms) are not deeply rooted
The microbial world, its limits and our search for life elsewhere EXTREMOPHILES – Organisms that live in the most extreme environmental condiFons (Temperature, salinity, pH, pressure, radiaFon, heavy metals, low water acFvity, and combinaFon of extremes) Important note: There is sFll much we don’t understand about Earth life and the limits of evoluFon of carbon‐based life to live under extreme condiFons
EvoluFonary innovaFons observed in Earth organisms THERE IS STILL MUCH TO BE DISCOVERED • During the past 10 years the Census of Marine Life has discovered thousands of new species of animals and plants • This is even more pronounced for marine microorganisms and it is estimated that more than 99% of the microbes in the ocean are uncharacterized new species
The microbial world, its limits and our search for life elsewhere EXTREMOPHILES – Organisms that live in the most extreme environmental condiFons (Temperature, salinity, pH, pressure, radiaFon, heavy metals, low water acFvity, and combinaFon of extremes)
Why study extremophiles? • Limits of carbon‐based life • Some extremophiles deeply rooted in global phylogeneFc trees (parFcularly thermophiles) • The range of habitat condiFons for extremophiles may be analogous to environmental condiFons on other planets and moons • Paleomicrobiology (metabolic history) and the changing environmental condiFons throughout Earth history • “Top down” approaches to studying the origin of life
Limits of Life Parameter Extreme range on Extreme level for growth Earth of organisms ~-50 - >1200°C Lowest Temperature -15°C Temperature Highest Temperature - 122°C Eukaryotes to 62°C ;metazoans to ~50°C 0 - 14 Bacteria, Archaea and fungi at pH 0 - 13 pH Distilled H 2 O to total dryness Highest salt - 35% NaCl (many microbes Water activity and animals can survive desiccation) (A w ) Generally less than 1 kGy Some microbes survive levels 10X Radiation higher than found naturally on Earth Depends on environments Bacteria and algae grow in 2-5mM Cd, Heavy metals and specific metals (>10mM) Zn, Ni etc <1 to ~1,100 atm High diversity of bacteria, invertebrates Pressure (subseafloor habitas possibly and fish in ocean trenches to >6 km in the crust)
Limits: Some key environmental variables regulaFng life processes • Temperature and Pressure : Together they determine the boundary condiFons for liquid water • Salinity : relates to the availability of water and in combinaFon with pressure or low temperature can result in added stress to cells • pH : in most cases organisms evolve mechanisms to maintain pH’s near neutrality inside the cell • Organic solvents : destroys lipid membranes • Other combina.ons: dryness, radiaFon, redox condiFons, heavy metals, etc in combinaFon with T, P, S, and pH
What are the limits for C‐based life? Only temperature and availability of water limit Earth life Note: toxic levels of metals, radiaFon, etc can kill life
Temperature range for microbial growth and survival: 1. Microbial growth at ‐15°C and up to at least 122°C 2. Enzyme acFvity at low temperature depends on liquid solvent Viable microbes observed at 250°C 3. Salts and extracellular polysaccharides (EPS) can protect cells; some (122°C) hyperthermophiles have >4M K at high temperatures 4. Bacterial spores and vegetaFve Maximum growth T for eukaryotes (70°C) cells have been observed from Maximum growth T for metazoans (~50°C) million year ice cores 5. Anaerobes including methanogens (along with methane) in ice cores 6. Anaerobic methane oxidizing Enzyme acFvity in water/organic solvent mixture archaea associated with (Bragger et al., 2000) methane hydrates (Modified from Deming and Eiken, 2007)
Temperature Classes of Microorganisms
Hyperthermophile (Temp. OpFmum >80°C) – Early microbiology studies pioneered by Thomas Brock in the 1970’s Octobus Springs, Yellowstone NaFonal Park (The site where Thermus aqua;cus was Boulder Spring, isolated. T aqua;cus provides the Yellowstone NaFonal polymerize enxyme used in the Polymerase Park Chain ReacFon)
Hydrothermal vents discovered 1977, black smokers, 1979 Juan deFuca Ridge – NE Pacific (2,500 m depth, 350°C hot fluid)
Different Edifice Morphologies, Endeavour
Highest Temperature Organism on Earth from Finn (Mothra) Highest Temperature Organism on Earth from Finn 3 days growth 2 m 121°C organism grown under anaerobic condiFons with acetate, FeIII forms magneFte, doubles 24 hrs 1.03 m Kashefi et al., Science 2003
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