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Archaea

Archaea. Extremophiles Evolutionarily Primitive Formerly known as Archaeabacteria. History. Originally grouped with Bacteria Recognized in 1977 Carl Woese and George Fox 16S rRNA sequencing Greek archaea “ancient”

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Archaea

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  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 viruesand 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

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