Life in extreme environments

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Life in extreme environments

• MBB323 Guest Lecture
• September 24, 2003
• Dr. I.V. Kovalyova
• SBB 8146

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Living on the edge?

• Physical extremes (T, p, radiation, gravity,
  vacuum) and geochemical extremes (desiccation,
  salinity, pH, oxygen species, redox potential,
  concentration of heavy metals, etc)
• Also, biological extremes (nutritional extremes,
  population density, infection, etc.)
• Taxonomic range spans all three domains of life
  (Archaea, Bacteria, and eukaryotes)

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Examples of extreme ecosystems

• Hotsprings and geysers (hot water and steam, low
  pH, noxious elements such as mercury, arsenic)
  martian lakes?
• Deep sea high p, cold T, except in the vicinity
  of hydrothermal vents (400?C, high p, pH3-8,
  unusual chemistry) prebiotic chemistry
  compatible to that thought relevant to the origin
  of life
• The closest organism to the common ancestor on
  the tree of life is a thermophile
• Hypersaline environments salt flats, evaporation
  ponds, natural lakes (Great Salt Lake) and
  dead-sea hypersaline basins dominated by
  halophilic archaea, including square bacteria D.
  salina
• Evaporite deposits bacteria get trapped in fluid
  inclusions of growing NaCl and other crystals and
  can survive for millions of years
• Deserts extremely dry, cold, or hot (dry valleys
  of Antarctica, Atacama Desert)
• Ice, permafrost and snow
• Atmosphere (panspermia?)
• Space
• Other planets

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Extreme Life Briefing

• Hottest 235 F (113?C) Pyrolobus fumarii (Volcano
  Island, Italy)
• Coldest 5 F (-15?C) Cryptoendoliths (Antarctica)
  
• Highest Radiation (5 MRad, or 5000x what kills
  humans) Deinococcus radiodurans
• Deepest 3.2 km underground
• Acid pH 0.0 (most life is at least factor of
  100,000 less acidic) pH 5-8
• Basic pH 11.0 (most life is at least factor of
  1000 less basic) pH 5-8
• Longest in space 6 years Bacillus subtilis (NASA
  satellite)
• High Pressure (1200 times atmospheric)
• Saltiest 30 salt, or 9 times human blood
  saltiness. Haloarcula

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How?

• Our anthropocentric definition of extreme
• To maintain chemistry in an aqueous environment
  (life as we know it), cells need certain
  temperatures (thermodynamic principles), pH and
  solutes, control over biomolecules and electric
  currents regulation, ability to repair damage,
  etc. etc.
• Think of desiccation, radiation, increased
  pressure, reactive oxygen species for example
  these and other extreme conditions are able to
  effectively damage and destroy biomolecules

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Tolerance vs loving

• Are organisms in such environments subsisting and
  merely getting by or are they really thriving?
• Is an organism an extremophile under all
  conditions or does it have the ability to adapt?
  What about stages of growth? (think of
  sporulation which is when organisms are far more
  resistant to environmental extremes)

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Life as we know (?) it

• Liquid water is required for life on Earth
• An input of energy is required for life on Earth
• Control of the energy flow is required for life
  on Earth
• Life is based on organic chemistry, therefore
  such chemistry must be allowed to operate (redox
  chemistry is universal)

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Temperature

• Low T - ice crystals induce structural
  devastation unless you have anti-freeze proteins
• High T denaturation of biomolecules (proteins
  and nucleic acids), increase the fluidity of
  membranes
• T influences solubility of gases in water and is
  therefore important for aquatic organisms
  requiring O2 or CO2
• Range from lt15?C to gt80?C
• Most hyperthermophilic organisms are archaea
  Pyrolobus fumarii growing at the highest known
  temperatures of up to 113?C
• Hyperthermophilic enzymes actually have an even
  higher temperature optimum, i.e. 142?C for
  amylopullulanase
• Upper limit for eukaryotes is 60?C (protozoa,
  algae, fungi), 50?C (mosses), 48?C (vascular
  plants), fish (40?C) (low solubility of O2 at
  high temperature!!!)
• Can preserve microbes and cell lines at -196?C,
  but the lowest temperature for active microbial
  metabolism is -18?C

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Pressure

• we exist under 1 atmosphere101kPa1.013bar and
  1g
• our aquatic ancestors evolved under hydrostatic
  pressure
• Hydrostatic pressure increases at a rate of 10.5
  kPa per metre depth, compared with 22.6 kPa per
  metre for lithostatic pressure
• Pressure decreases with altitude at 10km above
  sea level, atmospheric pressure is almost ¼ of
  that at sea level
• The boiling point of water increases with
  pressure, so water at the bottom of the ocean
  remain liquid at 400?C
• So, increased pressure can increase the optimal
  temperature for microbial growth!

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Pressure (continued)

• Pressure also changes volume changes
• Pressure compresses packing of lipids resulting
  in decreased membrane fluidity
• If a chemical reaction increases in volume, it
  will be inhibited by an increase in pressure
• Sudden pressure can be lethal diving!
• So, amazingly, the worlds deepest sea floor at
  almost 11 km (the Mariana trench) harbors
  organisms that can grow at standard temperature
  and pressure as well as obligatory piezophilic
  species (can grow at 70-80 MPa, but not below 50
  MPa)
• Change in g include changes in biomass
  production, an increase in conjugation and
  changes in membrane permeability (launch
  vehicles, International Space Station, the Moon,
  Mars)

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How do organisms respond to pressure?

• Pressure-sensing has been analyzed among
  barophile branch bacteria by searching for genes
  activated by high pressure
• A pressure-regulated operon contained genes
  homologous to those encoding Omps (outer membrane
  proteins), ToxR and ToxS environmental sensor
  proteins (pH, temperature, osmolarity) in other
  organisms as well as proteins of unknown function
• Evidence indicates that pressure-sensing depends
  on the physical state of the cytoplasmic membrane

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Radiation

• Particles (neutrons, electrons, proteins, ?
  particles and heavy ions) or electromagnetic
  waves (? rays, UV, Vis, IR, microwave, radiowave)
• Importance in medicine high UV and ionizing
  radiation
• High levels range from decreased motility to
  inhibition of metabolism, damage to nucleic
  acids, damage through the production of reactive
  oxygen species
• Deinococcus radiodurans can withstand ionizing
  radiation up to 20 kGy of ? rays and UV up to
  1000 J m-2
• This resistance is though to be a by-product of
  resistance to extreme desiccation
• Other organisms Rubrobacter species and the
  green algae Dunaliella bardawil

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Desiccation

• Liquid water essential solvent for life
• High melting and boiling points with a wide
  temperature range over which it remains liquid,
  dipole character O-H hydrogen bonds
• Water limitation constitute an extreme
  environment (remember August BC fires, recent
  Vancouver draught)
• Organisms can tolerate extreme desiccation by
  entering a state with little intracellular water
  and no metabolic activity called anhydrobiosis
• Bacteria, yeast, fungi, plants, insects,
  tardigrades, mycophagous nematodes, shrimp

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pH

• pH -log H
• Physiological pH7 (again, very biased)
• Proteins denature at low pH
• Acidophiles and alkaliphiles
• Ferroplasma acidarmanus has been described
  growing at pH0 in acid mine drainage in Iron
  Mountain California H2SO4, high Cu, As, Cd, Zn
• If pH is low, H are hard to come by, therefore
  life can be energetically difficult (recall ATP
  synthases and proton gradient)

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Oxygen

• Aerobic (O2-based) metabolism is far more
  efficient than anaerobic but oxidative damage can
  be very serious (ageing, cancer, etc.)
• Photochemical production of H2O2 by UV within
  cells (endogenous) and in aquatic systems
  (exogenous)
• Mitochondrial respiration, cytochrome metabolism
  of hydroperoxides, oxidative bursts used to fight
  pathogens in animals and plants
• The presence of oxygen can enhance
  radiation-induced DNA damage

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How?

• Keep external environment out (heavy
  metal-resistant bacteria use an efflux pump, some
  acidophiles keep their cytoplasms neutral by
  active pumping of H out)
• Research has focused on nucleic acids, membrane
  lipids, and proteins
• DNA, RNA, lipid, proteins structure linked to
  function vulnerability to high T, radiation,
  oxidative damage, desiccation

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How?

• Membranes adjust their membrane compositions when
  temperatures are shifted to maintain optimal
  membrane fluidity
• Proteins in response to T increase ion-pair
  content, form higher-order oligomers, decrease
  flexibility, decrease the length of surface loops
  that connect elements of secondary structure,
  anti-freeze proteins in cold-water fish, optimize
  electrostatic and electrophobic interactions
• DNA monovalent and divalent salts enhance the
  stability of nucleic acids, GC content (A-T vs
  G-C)
• In response to radiation production of
  antioxidants, detoxifying enzymes, repair
  mechanisms
• In response to pH and salinity osmotic balance
  via ionic fluxes

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Summary

• Extremophiles are organisms capable of thriving
  at extreme physical and chemical conditions
• A number of molecular mechanisms have been
  discovered that enable extremophiles to function
  properly at extreme conditions, but the research
  is still very new and exciting
• Humans can benefit from extremophiles through
  biotechnology and bioremediation
• Understanding how extremophiles function is
  useful for tracing evolutionary processes and
  even predicting them elsewhere, life on other
  planets (Europa, Mars, etc.)

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Suggested readings and web links

• Rossi M, Ciaramella M, Cannio R, Pisani FM,
  Moracci M, Bartolucci S. (2003) Extremophiles
  2002. J Bacteriol. 185(13)3683-9.
• Rothschild, LJ and Mancinelli, RL (2001) Life in
  extreme environments. Nature, 409 1092-1101 (and
  references therein).
• de la Torre JR, Goebel BM, Friedmann EI, Pace NR.
  (2003) Microbial diversity of cryptoendolithic
  communities from the McMurdo Dry Valleys,
  Antarctica. Appl Environ Microbiol.
  69(7)3858-67.
• Harris JK, Kelley ST, Spiegelman GB, Pace NR.
  (2003) The genetic core of the universal
  ancestor. Genome Res. 13(3)407-12.
• DeLong EF, Pace NR. (2001) Environmental
  diversity of bacteria and archaea. Syst Biol.
  50(4)470-8.
• Pace NR (2001) The universal nature of
  biochemistry. (2001) Proc Natl Acad Sci U S A.
  98(3)805-8.
• NASA Astrobiology Institute http//nai.arc.nasa.go
  v/
• Astrobiology web on Extremophiles
  http//www.astrobiology.com/extreme.html
• Queens Astrobiology Club
• http//qlink.queensu.ca/8ivk/Club1.html