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CU-Boulder EBIO 3400 - Archaea
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Archaea Are Often Thought ofas Extremophiles, but many are notPyrobolus-a thermophilic Archaeon that grown best above the bp of water!Some archaea can liveWITHIN granules ofsalt!Similarities:• Archaea have generally the same shape, size,and appearance as bacteria.• Like bacteria, Archaea multiply by binaryfission and move primarily by means offlagella.• These morphological similarities can make itdifficult to visually tell a bacterium and anarchaean apart.• Additionally, archaea are more phylo-genetically similar to eukarya than bacteriais to either of them.Similarities and Differences cont.Differences• Unlike bacteria, archaea cell wallsdo not contain peptidoglycan.Chemistry of cell walls is different from bacteria: archaealcell walls don’t contain peptidoglycan. Archaea have varioustypes of cell wall including pseudopeptidoglycanNo D-amino acidsDifferences• Unlike bacteria, archaea cell wallsdo not contain peptidoglycan.• Archaea have different membranelipid bonding compared to Bacteriaand Eucarya.Archaea membrane lipids have etherbonds instead of ester bondsR-C-O-C-R = ETHER BOND = ARCHAEAR-C-O-C-R = ESTER BOND = BACTERIA & Eucarya=OArchaeal lipids lack the fatty acidsfound in Bacteria and Eukaryotes andinstead have side chains composed ofrepeating units of isoprene.H2C=C-C=CH2 HCH3ISOPRENE--Structure of the tetraether lipoglycan of the plasmamembrane of Thermoplasma acidophilum. Note that thisis not a lipid bilayer and the hydrophilic group is apolysaccharide rather than a phosphate group.Membranes revisitedLipid bilayer as seenin some Archaea andall Eucarya andBacteria ---->Lipid monolayer asfound only in someArchaea -especiallyin extremethermophiles ---->Differences• Unlike bacteria, archaea cell wallsdo not contain peptidoglycan.• Archaea have different membranelipid bonding from bacteria andeukarya.• There are genetic differences.Other differences• Like Bacteria, Archaea have 70S ribsomes,but they have a different shape.•Archaea have more complex RNA polymerases than Bacteria, similar to Eucarya.Differences• Unlike bacteria, archaea cell walls do notcontain peptidoglycan.• Archaea have different membrane lipidbonding from bacteria and eukarya.• There are genetic differences.• Archaea have different metabolic pathways.Metabolic differences:• Archaea are very metabolically diverse, sothey are hard to generalize.• Archaea do not use glycolysis pathway tobreak down glucose (though they do usesimilar pathways).• Many archaea do not have functional Kreb’scycle pathways (but some do).The Taxonomy of ArchaeaThe domain Archaea is divided into 2 main divisions (orkingdoms):• Crenarchaeota• EuryarchaeotaArchaea: major metabolic groups =methanogens, halophiles, and sulfurmetabolizers• KorarcheotaEuryarchaeota• Occupy many different niches and have adiversity of metabolic patterns• Include the methanogens, the extremehalophiles, the sulfate reducers, and manyextreme thermophiles.Euryarchaea also have representative methanogens, halophiles, and sulfur metabolizersThe Euryarchaea - 5 major groups:1) Halophiles2) Methanogens3) Thermoplasms4) Extreme Thermophilic S0 metabolizers5) Sulfate - ReducersExtremely Halophilic Archaea• live in habitats that are highly saline(requires at least 9% NaCl for growth,may tolerate near saturation - 32%)> Dead Sea> Great Salt Lake> Heavily salted foods•Most extreme halophiles are chemoheterotrophic Some extreme halophiles are capable of light mediatedsynthesis of ATP that does NOT involve chlorophyll. i.e. a pathway that uses the sun’s energy to make ATP. Methanogens• produce methane (CH4) as part of energymetabolism.• Occupy diverse habitats:> Marshes and swamps> Animal digestive tracts> Hydrothermal vents> Waste Management facilitiesMethanogens are strictly anaerobic.The basic chemical reaction most methanogens use:CO2 + 4H2CH4 + 2H2OOther substrates may also be used such asformate (CO2 + H2O in a combined form)COMethyl substrates, e.g. methanol (CH3OH)Acetrotrophic substrates, e.g. acetate (CH3COO-)In any of those cases, the production ofmethane is an exergonic reaction, thus theenergy can be used to synthesize ATP.If the organisms use CO2 as a carbon source,they are classified as autotrophs.Methanogens live in the guts of manyorganisms, from termites to humans.Many methanogens live symbiotically withfermenting bacteria.Some even live endosymbiotically with anaerobicprotozoans.The methanogens use up the H2 generated by aspecial organelle called the hydrogenosome.Rumen ArchaeaAnimals that eat primarily cellulose, i.e. grazers,often use methanogenic archaea to help digestion.Ruminants (cows, sheep,deer, camels) havecompartmentalizedstomachs that permitanaerobic archaea tothrive.Cows can produce up to 600 liters ofmethane every day!This accounts for about 15% of global methaneproduction and is a serious problem for global warming.ThermoplasmsThese organisms thrive at extremetemperatures and/or acidities.ex.• Thermoplasma - lives in refuse piles of coalmines.* Lacks a cell wall• Picrophilus - extreme acidophile - optimumgrowth at pH 0.7 and reported to grow at pH -0.67!Structure of the tetraether lipoglycan of the plasmamembrane of Thermoplasma acidophilum. Note that thisis not a lipid bilayer and the hydrophilic group is apolysaccharide rather than a phosphate group.CrenarchaeotaThought to resemble the ancestor of archaeaAlmost all the best described ones arethermophiles or extreme thermophiles……though some mesophilic forms have recentlybeen discovered in the ocean - dominant form oflife below 300 meters in the oceans!Crenarcheota• most are strict anaerobes• common in Yellowstone and deep sea volcanoes• 2 important genera are Sulfolobus andThermoproteus•Can be chemoheterotrophic or chemoautotrophicKorarcheota- only recently discovered (1996) in Yellowstonehot spring - Obsidian Pool• using environmental sampling of rDNA, 19 newtaxa were discovered, including 2 that branchedprior to the diversification of all other ArchaeaHow do these organisms survive at such hightemperatures?• Protein stability• DNA stability• Lipid stability• covalent bonds in hydrophobic ends of lipidscreate a lipid monolayer instead of a lipidbilayer - less likely to be pulled apart.• many proteins have similar amino acid compositionas those of mesophilic bacteria, but are foldeddifferently to make them more heat stable.• they tend to have more chaperonins (= heat shockproteins)


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CU-Boulder EBIO 3400 - Archaea

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