Archaea
Extremophiles
Evolutionarily Primitive
Formerly known as Archaeabacteria
History
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Originally grouped with Bacteria
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Recognized in 1977
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Carl Woese and George Fox
16S rRNA sequencing
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Greek archaea “ancient”
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Common ancestor thought to be a simplistic prokarya
with poorly organized genetic material
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Thought to be involved in evolution of Eukarya-not
accepted
Morphology
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Spherical, rod-shaped, spiral, lobed,
filamentous, or rectangular
Morphology
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0.1-15 microns
Single circular chromosome
Single cell membrane
Flagella
No organelles
Ecology
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Extremophiles (coined 1974)
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Thermophiles (up to 113C)
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Psycrophiles
Acidophiles and Alkaliphiles
Halophiles
Some combine extremes, ie Picrophilus (~60C and
0.5pH)
Methanogens
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Black smokers
Geysers
Often found in the guts of ruminants, termites and
even humans
Found in all known environments
Adaptations to Extremes
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In extreme pH must avoid hydrolysis of proteinsachieved by changing internal pH
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Anaerobes do not maintain stasis, while aerobes do
Specific enzymes are active at optimal pH
Structure of cell membrane stabilized in high
temperature environments by:
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Allows for formation of carbon rings which increases
stability
Ether linkage is less reactive than ester linkage
Tetraether molecules
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Can form monolayers (Sulfolobus and Thermoplasma)
Adaptations to Extremes
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Protection of genetic material
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High salt concentrations in cytoplasm
DNA binding proteins similar to eukaryotic histones
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Share amino acid homology
MC1-Methanosarcinaceae
HMf-Methanobacteriales
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Organizes DNA in sturctures similar to chromatin
Allows for positive supercoiling
Eukarya have negative supercoiling (nucleosome)
HTa-Thermoplasma
HTa (like)-Sulfolobus
Evolution
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Primitive form
Related to Eukarya
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tRNA
Ribosomes
TATA binding proteins and TFIIB (transcription)
Similar initiation and elongation factors for translation
Similarities to bacterial genetic material
Evolution
Phyla
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Based on rRNA sequences
Originally two groups
Currently three recognized
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Crenarchaeota
Euryarchaeota
Korarchaeota
Crenarchaeota
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Rod, spherical, filamentous, and oddly shaped cells
Organotrophic and lithotrophic
Most are anaerobes
Lack histone like proteins
Some sulfur dependent (as electron acceptor or donor)
Thermophiles (82-110 Celcius; up to 113C known)
Thermoacidophiles
Psycrophiles
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Discovered when lipids of composition similar to other archaea
were found in ocean water
Could be a major contributor to global carbon fixation
Genera
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Sulfolobus, Desulfurococcus, Pyrodictium, Thermoproteus,
Thermofilum
Euryarchaeota
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Broad ecological range
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Thermophilic aerobes and anaerobes
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Pyrococcus and Thermococcus S-metabolizers
Extreme Thermophilic
Sulfate reducing archaea
Thermoplasms
Halobacteria
Methanogens
Euryarchaeota
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Extreme Thermophilic S-metabolizers
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Thermococci (anaerobic)
Reduce sulfur to sulfide
Flagellated
(80-100 Celcius)
Archaeoglobi
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Sulfate reducing archaea
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Thermophilic
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Sulfate, sulfite, thyosulfate into sulfide
Including marine thermal vents
Has cell wall with glycoprotein subunits
Gram negative
Euryarchaeota
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Thermoplasms
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Thermoacidophiles that lack cell walls
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Cell membrane strengthened by various proteins
55-59 Celcius at pH 1-2
May be aerobic
May be flagellated
Mine refuse piles
Euryarchaeota
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Halobacteria
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Halobacterium and Haloferax
Dependent on high salt concentrations
Aerobic
Some flagellated
Chemoherterotrophs with respiratory metabolism
Some use light to form ATP (not photosynthesis-no
chlorophyl)
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Rhodopsin (4 types)
Euryarchaeota
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Methanogens
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Methanosarcina
Themophilic varietes (84-110 Celcius) including
Methanobacterium, Methanococcus, Methanothermus
Anaerobics
Convert carbon dioxide, hydrogen gas, menthanol,
acetate to methane (and carbon dioxide) for energy
Autotrophic
Survive in conditions similar to those of a young Earth
Korarchaeota
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Recently discovered in terrestrial geysers
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Yellowstone
Separation supported by 16S rRNA
sequencing
Evolutionary divergence from within
Crenarchaeota or from before divergence
of Crenarchaeota and Euryarchaeota
Unique characteristics of Archaea
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Cell membrane
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Single layer
Pseudopeptidoglycan or protein
L-glycerol (stereoisomer)
Ether linkage (C-20 diether lipids)
Some tetraether molecules (C-40 tetraether lipids)
Branching hydrophobic side chain
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Carbon ring formation
Resistant to lysozyme and beta-lactam antibiotics
Flagella have unique composition and
development
Cell Membrane
Unique Characteristics
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Metabolic differences
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ADP dependent kinase (not ATP)
Pyrophosphate-linked kinases (not pyrophosphate
dependent phosphofructokinases)
Organotrophs, autotrophs, and an unusual form of
photosynthesis
No Archaea uses the full respiration or photosynthetic
cycles, but instead employs many of the steps
individually
Methanogens and some extreme thermophiles use
glycogen instead of glucose
Unique Characteristics
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Intracellular bodies
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rRNA (16S) sequence
tRNA
Plasmids
Lack of organelles (similar to bacteria)
Unique Characteristics
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Genetic Material
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Resistance to denaturation by heat seen in
thermophiles
Similar structure to bacteria
Some sequencing has revealed sections of DNA that
are shared with bacteria (gene sharing between
bacteria and archaea?)
Primary protein sequence is similar to Eukarya
Genes with similar functions organized together
(similar to operons)
Introns are found in rRNA and tRNA genes
Unique Characteristics
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Replication
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DNA Polymerase similar to that of eukaryotes,
eukaryal virues and E. coli
3’-5’ exonuclease (proofreading)
Restriction endonuclease
Topoisomerase
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Gyrase
Halobacterium halobium has reverse
transcriptase
Unique Characteristics
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Transcription
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RNA polymerase has up to 14 subunits (E. coli
has only 4) and is similar to eukaryotes
Requires general transcription factors to
initiate (like eukarya)
Promoters have an A-T rich sequence similar
to eukarya TATA box
Translation
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Signals similar to bacteria
Ending on a
historical
note…
re-enactment
of the
separation of
archaea from
bacteria
Sources
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Brown, J. R. and Doolittle, W. F. 1997. Archaea and the
Prokaryote-to-Eukaryote Transition. Microbiology and
Molecular Biology Reviews. 61 (4): 456-502.
Griffith University-http://trishul.sci.gu.edu.au/
Kevbrin, V. V., Romanek, C. S., Wiegel, J.
Alkalithermophiles: A Double Challenge from Extreme
Environments.
Microbiology 6th ed.
University of California Berkleywww.ucmp.berkeley.edu/archaea/archaea.html