Lecture 13' Extremophiles

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Lecture 13. Extremophiles

• What are extremophiles?
• Extremophilic micro-organisms
• Adaptive stresses
• Thermophiles
• Psychrophiles
• Halophiles
• Acidophiles
• Alkalophiles
• Radioresistance
• Barophiles
• Oligotrophs

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Extremophiles
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Adaptive stresses

• Thermophiles
• Psychrophiles
• Halophiles
• Acidophiles
• Alkalophiles
• Barophiles
• Radiophiles
• Oligotrophy

• Denaturation and chemical destruction of macro-
  and small molecules membrane hyperfluidity
• Membrane hypofluidity Slow reaction kinetics
• Hyperosmotic stress
• Chemical stability membrane potentials
• Proton pumping against a negative pH gradient
• Unfavourable reaction equilibria reaction
  kinetics
• Molecular damage
• Nutrient deficiency and uptake affinity

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Thermophiles to Hyperthermophiles
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Thermophilic biotopes

• Thermophiles desert soils, compost, industrial
  processing fluids (Bacillus, Clostridium,
  Streptomyces, Thermomyces, Caldarium)
• Extreme thermophiles terrestrial and shallow
  marine hydrothermal systems (Thermus, Sulfolobus,
  Thermococcus)
• Hyperthermophiles Deep sea hydrothermal vents
• (Aquifex, Pyrococcus, Pyrodictium,
  Methanococcus)

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Thermophilic biotopes
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Schematic diagram of a hydrothermal vent
Cold abyssal sea water super-saturated with O2
2-3oC
Ejection of mineral-rich anaerobic water into
oxic cold seawater massive precipitation of
oxidised metals and metal sulphides.
Temperature gradient provides niches for
hyperthermophilic to mesophilic chemoautotrophs
and heterotrophs
Reduced S and metal ions provide basis for
chemoautotrophs as first tier in complex trophic
structure
Superheated (lt450oC) water from km depths
Anaerobic, rich in metals and sulphide
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Living at high temperatures Problems and
Solutions

• Proteins denature at high temperatures.
• Many essential small molecules (e.g., ATP, NADH
  etc) are unstable at high temperatures.
• Membranes become more fluid at high temperatures.

• Thermodynamic stability of proteins is increased.
• Not known exactly metabolic channeling may be
  important.
• Membrane lipid compositions change to reduce
  fluidity.

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Psychrophiles living at low temperatures
Arctic, Antarctic, deep marine and alpine regions
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Organisms at low temperatures

• Psychrophiles Topt, 15oC, Tmax lt 20oC, Tmin ,
  lt0oC
• Psychrotolerants (psychrotrophs) Topt, 20oC,
  Tmax gt 20oC, Tmin , gt3oC
• Very wide species diversity of Bacteria, Fungi,
  Algae
• Limited diversity of Archaea

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PsychrophilesProblems and Solutions

• Low metabolic rates
• Membrane rigidity
• Protein flexibility
• Cytoplasmic freezing

• Grow slowly
• Adapt membrane fluidity
• gt Unsaturation
• lt Chain length
• gt Methyl branching
• Increase conformational flexibility
• Reduce intramolecular bonding
• Accumulation of solutes (freeze prevention)
• Ice-nucleating proteins (freeze control)

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Extreme halophiles

• Living at very high salt concentrations
• Vertebrates lt 1.5M
• Halobacteria 1.5 3M
• Haloarchaea 3 5.2M

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Extreme halophilesProblems and Solutions

• Osmoregulation
• Protein stability

• Archaea
• Accumulation of intracellular salts (5M KCl)
• Bacteria
• Accumulation of low molecular weight solutes
  (osmolytes) with osmotic potential
• Increases in acidic a.a.s

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Acidophiles

• Geothermal areas
• Acid mine drainage

pH 0 3
2So 3 O2 2 H2O à 2 H2SO4
4 FeS2 15 O2 14 H2O à 4 Fe(OH)3 8 H2SO4
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Acidophiles are phylogenetically diverse

• Eukaryotes
• Fungi (numerous)
• Algae (Cyanidium)
• Protozoa (flagellates, ciliates, amoebae)
• Bacteria
• Heterotrophs (Bacillus, Acidiphilium,
  Sulfobacillus)
• Autotrophs (Acidithiobacillus)
• Archaea
• Numerous heterotrophs and autotrophs, many
  thermophilic (Thermoplasma, Sulfolobus,
  Acidianus, Metallosphaera)

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AcidophilesProblems and Solutions

• pH homeostasis
• Molecular stability

• Intracellular pH trans-membrane potentials
• Internal pH is maintained at 5-7 by maintained
  by proton pumping high external proton drives
  chemiosmotic ATP synthesis
• Acid stable proteins
• Stabilised by increase in charged amino acids

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Alkalophiles

• Organisms growing optimally at pH 8.5 11
• Very widely distributed in the environment
• Prevalent in haloalkaline (soda) lakes
• Include bacteria, fungi, yeasts

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Problems and Solutions

• Na-dependent solute transport
• High affinity proton transport systems
• Reversed pH gradient
• Extracellular and periplasmic enzymes adapted to
  function at high pH

• High external Na
• Low external H
• High external pH
• Instability of external proteins

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Radioresistant organisms

• Ability to live in the presence of high levels of
  ionising radiation
• High energy radiation damages macromolecules
• DNA damage is most critical
• Deinococcus radiodurans can survive 3 MRad
  radiation (humans are killed by 100 Rad)
• Primary adaptation is a hyper-active DNA repair
  system (RecA)
• Many other DNA repair mechanisms

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Barophiles

• Organisms living at high pressures
• Barophiles versus barotolerants
• Organisms living in abyssal oceans
• High pressure affects the thermodynamics of
  reactions involving volume changes
• High pressure stabilises three-dimensional
  molecular structures

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Oligotrophy

• Growth at very low nutrient concentrations
• Oligotrophic environments are widespread
  (copiotrophic environments are relatively rare by
  comparison)
• Marine water contains 1-6 mg C.l-1 cf Nutrient
  Agar 4000 mg C.l-1
• Numerous species of bacteria, fungi and yeasts

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Problems and Solutions

• Low growth rates
• Low S concentrations
• Sudden changes in S concentrations

• Not a problem
• High affinity uptake systems (Ks values for
  glucose, acetate etc. lt 1 mM have been recorded).
• Oligotrophs have both H and L affinity uptake
  mechanisms