Archaea

1
Archaea

• Extremophiles
• Evolutionarily Primitive
• Formerly known as Archaeabacteria

2
History

• Originally grouped with Bacteria
• Recognized in 1977
• Carl Woese and George Fox
• 16S rRNA sequencing
• Greek archaea ancient
• Common ancestor thought to be a simplistic
  prokarya with poorly organized genetic material
• Thought to be involved in evolution of
  Eukarya-not accepted

3
Morphology

• Spherical, rod-shaped, spiral, lobed,
  filamentous, or rectangular

4
Morphology

• 0.1-15 microns
• Single circular chromosome
• Single cell membrane
• Flagella
• No organelles

5
Ecology

• Extremophiles (coined 1974)
• Thermophiles (up to 113C)
• Black smokers
• Geysers
• Psycrophiles
• Acidophiles and Alkaliphiles
• Halophiles
• Some combine extremes, ie Picrophilus (60C and
  0.5pH)
• Methanogens
• Often found in the guts of ruminants, termites
  and even humans
• Found in all known environments

6
Adaptations to Extremes

• In extreme pH must avoid hydrolysis of
  proteins-achieved by changing internal pH
• 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
• Allows for formation of carbon rings which
  increases stability
• Ether linkage is less reactive than ester linkage
• Tetraether molecules
• Can form monolayers (Sulfolobus and Thermoplasma)

7
Adaptations to Extremes

• Protection of genetic material
• High salt concentrations in cytoplasm
• DNA binding proteins similar to eukaryotic
  histones
• Share amino acid homology
• MC1-Methanosarcinaceae
• HMf-Methanobacteriales
• Organizes DNA in sturctures similar to chromatin
• Allows for positive supercoiling
• Eukarya have negative supercoiling (nucleosome)
• HTa-Thermoplasma
• HTa (like)-Sulfolobus

8
Evolution

• Primitive form
• Related to Eukarya
• tRNA
• Ribosomes
• TATA binding proteins and TFIIB (transcription)
• Similar initiation and elongation factors for
  translation
• Similarities to bacterial genetic material

9
Evolution
10
Phyla

• Based on rRNA sequences
• Originally two groups
• Currently three recognized
• Crenarchaeota
• Euryarchaeota
• Korarchaeota

11
Crenarchaeota

• 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
• Discovered when lipids of composition similar to
  other archaea were found in ocean water
• Could be a major contributor to global carbon
  fixation
• Genera
• Sulfolobus, Desulfurococcus, Pyrodictium,
  Thermoproteus, Thermofilum

12
Euryarchaeota

• Broad ecological range
• Thermophilic aerobes and anaerobes
• Pyrococcus and Thermococcus S-metabolizers
• Extreme Thermophilic
• Sulfate reducing archaea
• Thermoplasms
• Halobacteria
• Methanogens

13
Euryarchaeota

• Extreme Thermophilic S-metabolizers
• Thermococci (anaerobic)
• Reduce sulfur to sulfide
• Flagellated
• (80-100 Celcius)
• Archaeoglobi
• Sulfate reducing archaea
• Sulfate, sulfite, thyosulfate into sulfide
• Thermophilic
• Including marine thermal vents
• Has cell wall with glycoprotein subunits
• Gram negative

14
Euryarchaeota

• Thermoplasms
• Thermoacidophiles that lack cell walls
• Cell membrane strengthened by various proteins
• 55-59 Celcius at pH 1-2
• May be aerobic
• May be flagellated
• Mine refuse piles

15
Euryarchaeota

• Halobacteria
• 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)
• Rhodopsin (4 types)

16
Euryarchaeota

• Methanogens
• 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

17
Korarchaeota

• Recently discovered in terrestrial geysers
• Yellowstone
• Separation supported by 16S rRNA sequencing
• Evolutionary divergence from within Crenarchaeota
  or from before divergence of Crenarchaeota and
  Euryarchaeota

18
Unique characteristics of Archaea

• Cell membrane
• 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
• Carbon ring formation
• Resistant to lysozyme and beta-lactam antibiotics
• Flagella have unique composition and development

19
Cell Membrane
20
Unique Characteristics

• Metabolic differences
• 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

21
Unique Characteristics

• Intracellular bodies
• rRNA (16S) sequence
• tRNA
• Plasmids
• Lack of organelles (similar to bacteria)

22
Unique Characteristics

• Genetic Material
• 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

23
Unique Characteristics

• Replication
• DNA Polymerase similar to that of eukaryotes,
  eukaryal virues and E. coli
• 3-5 exonuclease (proofreading)
• Restriction endonuclease
• Topoisomerase
• Gyrase
• Halobacterium halobium has reverse transcriptase

24
Unique Characteristics

• Transcription
• 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
• Signals similar to bacteria

25
Ending on a historical note re-enactment
of the separation of archaea from bacteria
26
Sources

• 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 Berkley-www.ucmp.berkeley
  .edu/archaea/archaea.html