The Archaea

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• The Archaea
• wstafford_at_uwc.ac.za

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The ancient Archaea

• Archaea means "ancient" because use ancient
  energy mechanisms
• Many found in harsh, early earth-like
  environments.
• Typical biotopes
• Thermal vents at bottom of ocean
• extreme salt conditions (Great Salt Lake, Dead
  Sea).
• highly acid conditions.

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Unique features of the Archaea

• Antibiotics that affect Bacteria protein
  synthesis do not affect Archaea.
• Have a different cell wall chemistry - protein,
  glycoprotein, or polysaccharide
• Archaeal genes show sequence similarity to
  bacterial and eukaryotic genes
• Membranes structurally similar, but chemically
  unique
• a. Lipids are ether-linked (not ester-linked)
• b. Branched hydrocarbons and rings (not fatty
  acids)
• c. Glycerol may be attached at both ends
  (diglycerol)
• Archaea often live under extreme conditions
  (extremophiles)
• 1. High-temperature (near 105 C) hot springs
  rift vents
• 2. Alkaline or acid environments
• 3. Extremely saline conditions

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Biotopes of the Archaea

• Methanogens - strictly anaerobic. Methanococcus
  jannaschii , the first archaeal organism to have
  its genome sequenced
• Halophiles - require lots of salt for growth.
  Halobacterium --
• Found only in very concentrated brines,
  evaporating salt basins, Dead Sea, etc.
• Brightly colored due to purple pigments
  (bacteriorhodopsin)
• Use light energy to pump protons across cell
  membrane, generate proton gradient make ATP from
  this
• Hyperthermophiles- thermophiles, mostly
  anaerobic. Example Pyrococcus furiosis grows
  well at temperatures above boiling!
• Thermoacidophiles no cell wall placement
  uncertain
• Obligate parasite- Nanoarchaeum equitans

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Extreme Halophiles.

• Optimal NaCl concentrations for growth range from
  2 to 4.5 M (sea water is about 0.5 M). Found in
  Great Salt Lake, Dead Sea and salterns. The
  GC of the halophiles ranges from 60 to 71 and
  the best studied extreme halophile,
  Halobacterium, has a glycoprotein cell wall.
• Some halophiles have a novel form of
  photosynthesis bacteriorhodopsin which acts as a
  light driven proton pump.When oxygen is present
  Halobacterium salinarium cells grow
  chemoheterotrophically. Under anaerobic
  conditions, they produces patches of purple
  membrane- bacteriorhodopsin. Light causes the
  protein to undergo a conformational change that
  pumps protons across the membrane (this mechanism
  is similar to how our eyes transduce light
  signals). The proton gradient is used to generate
  ATP, which allows Halobacteriumto survive
  temporary oxygen limitation.

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Methanogens

• The methanogens are the most widely distributed
  of the Archaea and are most abundant in anaerobic
  environments (guts, swamps, sediments etc.). The
  GC of the methanogens ranges from 26 to 62,
  again indicating that this is a very diverse
  group.
• Methanogens all live in very reducing
  environments where e- acceptors like oxygen,
  nitrate and sulfate have been depleted and where
  even fermentable substrates have been mostly used
  up. In general these organisms are using H2 as
  their e- donor and CO2 as their e- acceptor.
• 4 H2 CO2 -----gt CH4 2 H2O
• Methanogens are important in the carbon cycle,
  supply of natural gas and in global temperature
  (methane is a greenhouse gas that causes global
  warming)

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Extreme thermophiles

• Distributed throughout the Archaea, optimal
  growth above 800C- adapted to environmental
  extremes similar to those that may have been
  present on earth when life evolved.
• It is also of ecological significance that the
  extreme thermophiles exist in environments that
  are hot, anoxic environments and therefore of
  metabolism that involve sulfur compounds etc.
• Because of their high thermostability, enzymes
  from thermophiles are being used in many
  commercial applications (laudry detergents with
  thermostable lipaes and proteseases, DNA
  polymerases used in polymerase chain reaction
  (PCR) and other molecular techniques that are
  carried out at high temperatures.

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Phylogenetic tree of the Archaea using 16S rRNA
gene as a molecular marker.
EURYARCHAEOTA CRENARCHAEOTA KORARCHAEOTA
NANOARCHAEOTA


Nanoarcheota
Nanoarchaeota
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Diversity of the Archaea

• Euryarchaeota. Many are Methanogens ( methane
  generators). They are most abundant in anaerobic
  environments (guts, swamps, sediments etc.) where
  e- acceptors like oxygen, nitrate and sulfate
  have been depleted and where even fermentable
  substrates have been mostly used up. Many use
  using H2 as their e- donor and CO2 as their e-
  acceptor. 4 H2 CO2 -----gt CH4 2 H2O
• Crenarchaeota All cultivated representatives are
  sulfur-dependent and thermophilic. However,
  mesophilic Crenarchaeota are approx. 50 of
  marine microbes below 100 meters depth in the
  oceans, so they may be among the dominant life
  forms on earth!! Recent studies also indicate
  that they very common in soils. A Crenarchaeote
  has been detected as a common symbiont in marine
  sponges.
• Korarchaeota and Nanoarcheota poorly sudied (few
  cultured representatives). Nanoarchaeum equitans
  is a thermophilic obligate symbiont of Igniococcus

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• and more unseen diversity
• To be discovered.