41 st Saas‐Fee course from Planets to Life 3‐9 April 2011 Lecture 3: 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) • Growth at low temperatures • Growth at high and low pH • Growth in high salt • Growth and survival in dry environments • Growth in extremely low nutrient environments
Was there only one tree of life on Earth? Does conFngency play a significant role in the origin of life as some think it did in the evoluFon of diversity of life forms? Eukarya Archaea Bacteria Only one tree of life Eukarya Archaea Bacteria Present tree of life is a branch of an exFnct tree Baross, 1998
(Deming, 2009) �
Psychrophiles • Lowest temperature for growth ‐12°C, acFve metabolism <‐22°C. • Evidence for survival at temperatures as low as ‐80°C (liquid nitrogen) • Spores found in ice cores that are >1 million years old
Psychrophiles: Temp max < 20ºC Marine sea ice Polaromonas ← Photos by Jim Staley → T opt = +4ºC Losest temperature for growth: Psychromonas ingrahami T opt = +4°C, T min = –12°C, T max = +10°C
Cultured phage‐bacterial host systems acFve at –1°C Middelboe et al., 2002 (seawater) Borriss et al., 2003 (sea ice) Wells and Deming, 2006 (both) 3 µm Colwellia psychrerythraea strain 34H 3 µm 3 µm (Borriss et al., 2003) (Wells and Deming, 2006)
Problems and Solutions: Psychrophiles Solutions � Problems � Prevent ice-crystal formation and cell Live in a briny habitat, produce death � compatible solutes and/or exopolysaccharides (EPS) � Make more flexible proteins Enable protein activity: enzymes must (higher α -helix; lower β - maintain significant catalytic sheet content) � activity at low temperature � Make more polar and less hydrophobic proteins, with fewer weak bonds (ionic, hydrogen) � Make lipids with greater content Maintain membrane function: the of short-chained, branched, organism must maintain and unsaturated fatty acids � significant levels of nutrient transport at low temperature �
“ I can see no limit to this power etc” (Darwin referring to natural selecFon” The Antarc>c ice‐fish (Channichthyidae) are the only known vertebrates without hemoglobin . Consequently, their blood is transparent. Their metabolism relies on the oxygen dissolved in the liquid blood and is absorbed directly through the skin from the water. This works because of the increased solubility of oxygen in cold water and is an adaptaFon to life at temperatures that are less than 0°C (icefish size 25 cm long) (Wikipedia)
Summary – Temperature and life • To date, the lowest temperature for growth is ‐12°C and the maximum temperature for growth is 122°C • Low temperature microbes (psychrophiles) do not have ancient lineages – Spore‐forming psychrophilic bacteria are of concern regarding planetary protecFon issues to icy planetary bodies • High temperature microbes (hyperthermophiles) have ancient lineages – Hyperthermophiles are of interest regarding the origin of life and the origin of metabolism and eukaryotes – The highest temperature for growth of a eukaryote is >60°C lower than the maximum temperature for a microbe
pH limits for life Natronobacterium Natronobacterium Ephydrid flies Bacillus firmus OF4 Heather sedges Cyanidium Spirulina Sphagnum Fungi Plectonema ProFsts Carp RoFfers Archaea Synechococcus Lost City methanogens 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Acid mine Soda lakes drainage; geo‐ pH range in hydrothermal vents thermal sulfur sites
Sulfolobus spp growat pH <1 Acidic mud pot in Yellowstone Park ‐ home to the acidophile Sulfolobus acidocaldarius Sulfolobus acidocaldarius is an hyperthermophile that grows in acid hot springs, mud pots etc at temperatures from 60‐100°C and at pH from <1‐5. EM is X85,000 and fluourescent photomicrograph shows S. acidocaldarius amached to sulfur. The organisms oxidizes S° to H 2 SO 4 S 0 + 1+ 1/2 O 2 + H 2 O → H 2 SO 4 Red coloraFon on rocks near Naples, Italy produced by the CO 2 → Cell material hyperthermophile Sulfolobus solfataricus
The record holder for growth at low pH Picophilis oshimae is an Archaea that can grow at ph of 0.06 and is incapable of growing at pH 3 or higher. P. oshimae growth Picrophilus oshimae at 45‐65°C and was isolated pH opt = 0.7 ( J. Bacteriol. 177: 7050, 1997) from solfutaric soils. This organisms cannot maintain membrane integrity at pH higher than 4
Growth curves of Picophilis osphimae Growth curves of P. oshimae at various pH values (OD = op>cal density) (from Puehler et al., J. Bacteriology 1995)
Unusual Characteristics of Acidophiles The genome of Picrophilus torridus ( PNAS 101:9091, 2004) reveals: 1. A very small genome ‐ the 1.55 Mbp P. torridus genome is near the smallest for free‐living heterotrophic aerobes. 2. High raFo of genes encoding Proton‐Motor‐Force ‐driven versus ATP‐driven transporters. 3. High coding density; ~91% of genome encodes protein. 4. Extremely acid‐stable membrane proteins. 5. Extensive respiratory systems are necessary because of energeFc needs plus the need to consume protons. Many genes encoding respiratory funcFons have been obtained by lateral transfer. Viruses of hyperthermophilic/acidophilic Archaea are extremely unusual ( Res. Microbiol. 154:474, 2003).
Problems and Solutions: Acidophiles Problems Solutions 1. Internal pH Remains above pH 4.5 due to impermeability of the cytoplasmic membrane; DNA hydrolysis would be a problem at lower cytoplasmic pH values 2. Protein Stability/Function Proteins in wall and membrane contacting high [H + ] are extremely acid-stable; cytoplasmic proteins must be somewhat acid-stable 3. Bioenergetics Proton motive force drives nutrient transport and ATP synthesis; ATP synthesis by ATPase is not a “free lunch”, since respiration requires electrons: 1/2 O 2 + 2 e – + 2H + → H 2
Coupling membrane Chemiosmosis Redox reacFons alternaFng H Chemical energy Light energy and e‐ carriers (REDOX H + (oxidaFve phosphorylaFon) ( photophos‐ PUMP) phorylaFon) H + H + H + H + ATPase H + Pump ATP An ion gradient has a potenFal energy and can be used to The “bare bones” of chemiosmoFc power chemical reacFons when coupling (Raven and Smith, 1978) the ions pass through a channel
Growth at high pH - Alkaliphiles: pH opt > 9 Record Holder: Natronobacterium magadii pH opt = 10; pH min = 8; pH max = 11.5 SODA LAKE CHARACTERISTICS NaCl → low to high SO 4 2– → low to high Mg 2+ , Ca 2+ → extremely low HCO 3 – /CO 3 2– → extremely high pH → 9–12 Lake Hamara, Libyan Desert, Egypt (Madigan)
Properties of Alkaliphiles 1. Diversity: a. Many uncultured (presumably alkaliphilic) Bacteria and Archaea exist in halo‐alkaline habitats ( Extremophiles `````8:63, 2004). b. Many alkaliphiles are species from well‐known phyla of Bacteria and Archaea . 2. Alkalithermophiles: a. Many rapidly growing alkalithermophiles are known and some have generaFon Fmes as short as 10 minutes. b. Some alkalithermophiles are also halophiles–the first “triple extremophiles” known (temperature, salt, pH). Overview of Alkaliphiles: Prokaryotes 2: 283, 2006
Problems and Solutions: Alkaliphiles Problems Solutions 1. Internal pH Remains below pH 9.5 due to impermeability of the cytoplasmic membrane; RNA hydrolysis would be a problem at higher cytoplasmic pH values 2. Protein Stability/Function Proteins contacting the environment are stable to alkali and alkaliphilic; have applications as laundry proteases, lipases 3. High Salt Many alkaliphiles are also halophilic Na + gradient (instead of H + gradient) 4. Bioenergetics drives motility and transport, but a proton-motive force drives ATP synthesis
Mono Lake in California is very alkaline at pH 10 (2.5g NaOH/liter). The towers consist of calcium carbonate (FW mixes with alkaline springs). Towers can be 10 m high. The salinity of Mono Lake is about 8.5% salts. Brine shrimp and a diverse groups microorganisms live in the lake.
Science 2008
Arsenic driven photosynthetic bacteria discovered at Mono Lake New Electron Donor for CO 2 FixaFon Cyanobacteria and green plants get their electrons from H 2 O Anoxygenic photosyntheac bacteria use : H 2 , H 2 S, Fe 2+ , NO 2 – , ‐ now arsenite (AsO 3 ‐2 ) (Calvin Cycle: 6 CO 2 + 24 H → C 6 H 12 O 6 + 12 H 2 O)
Other electron donors include H 2 , FeII, Arsenic The pelagic ocean Hydrothermal vents* PosiFon of chemosynthesis within autotrophic metabolism. Instead of light, the energy required for the reducFon of CO 2 to organic‐ carbon (CH 2 O) by photosyntheFc organisms, vent microbes use chemical energy including hydrogen sulfide (H 2 S) *Besides the use of hydrogen sulfide as an energy source, some microorganisms use hydrogen and methane gas or some metals like iron and manganese as sources of energy
AsO 3 2– → AsO 4 2– + 2 e ‐ Arsinite Arsinate These electrons are available for photosynthesis by microbes in Mono Lake (Science 2008)
Can arsenic subsFtute for phosphate in nucleic acids? 2010
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