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) Methanogens
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 ( 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 Extreme Thermophilic
Thermophilic aerobes and anaerobes
Pyrococcus and Thermococcus S-metabolizers
Extreme Thermophilic
Sulfate reducing archaea
Thermoplasms
Halobacteria
Methanogens

13. Euryarchaeota Extreme Thermophilic S-metabolizers Archaeoglobi
Thermococci (anaerobic)
Reduce sulfur to sulfide
Flagellated
( 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 ( 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 Archaea and the Prokaryote-to-Eukaryote Transition. Microbiology and Molecular Biology Reviews. 61 (4):
Griffith University-
Kevbrin, V. V., Romanek, C. S., Wiegel, J. Alkalithermophiles: A Double Challenge from Extreme Environments.
Microbiology 6th ed.
University of California Berkley-