Questions and Answers
The phylogenetic tree of Archaea is constructed based on comparative sequences of ______ proteins.
ribosomal
The exact ancestry of Archaea groups remains a ______ issue.
contentious
All Archaea have ______-linked lipids in their cell membranes.
ether
Archaea lack ______ in their cell walls.
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Chemoorganotrophy is a widespread metabolic process among ______.
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Hydrogen (H2) is a common ______ donor in chemolithotrophic metabolisms.
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ELEMENTAL ______ (S0) is a common electron acceptor in anaerobic respiration.
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Methanogenesis is a globally important process that is only present in ______.
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Archaea are also well known for containing many species of ______, including species that are hyperthermophiles
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A great many species in the ______ and most Thaumarchaeota are not extremophiles and are found in soils, sediments, oceans, lakes, in association with animals, and even in the human gut.
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The phylum ______ comprise a large and physiologically diverse group of Archaea.
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Methanogens are the strictest of ______ while extreme halophiles are primarily obligate aerobes.
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The hyperthermophilic methanogen ______ is an example of a euryarchaeote.
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The cell wall–less ______ is an organism phenotypically similar to the mycoplasmas.
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Extremely halophilic Archaea, often called the “______”, are a diverse group that inhabits environments high in salt.
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The key genera of extremely halophilic Archaea include ______, Haloferax, and Natronobacterium.
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Methanogens show a diversity of ______ wall chemistries.
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Physiologically, methanogens are obligate ______, and strict anoxic techniques are necessary to culture them.
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Most methanogens are ______ and nonhalophilic, although species that grow optimally at very high or very low temperatures, at very high salt concentrations, or at extremes of pH, have also been described.
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Several substrates can be converted to ______ by methanogens.
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Compounds such as ______ can be converted to CH4, but only in reactions in which methanogens and other anaerobes cooperate.
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Three classes of compounds make up the list of ______ substrates shown in Table 2.
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CO2-type substrates include CO2 itself, which is reduced to ______ using H2 as the electron donor.
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The reactions of ______ production are summarized in the following equations:
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The term ______ is used to indicate that these organisms are not only halophilic, but that their requirement for salt is very high.
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Many Euryarchaeota are ______, microorganisms that produce methane as an integral part of their energy metabolism.
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Such salty habitats are called ______.
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An organism is considered an ______ if it requires 1.5 M (about 9%) or more sodium chloride for growth.
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The reaction CH4 + 3HC03- --> 4HC02- + H20 + H is a process of ______ respiration.
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Thermoplasma, Ferroplasma, and Picrophilus are highly ______ and thermophilic microorganisms.
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______ is the terminal step in the biodegradation of organic matter in many anoxic habitats in nature.
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Thermoplasma has a unique cytoplasmic membrane structure that contains a ______ material called lipoglycan.
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Some phylogenetic relatives of extremely halophilic Archaea, for example species of ______ and Natronobacterium, are able to grow at much lower salinities.
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The lipoglycan in Thermoplasma's membrane consists of a ______ lipid monolayer with mannose and glucose.
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The taxonomy of methanogens is based on both ______ and phylogenetic analyses.
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Thermoplasma is a facultative ______, growing either aerobically or anaerobically by sulfur respiration.
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Methanogens show a variety of ______.
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Archaeoglobus was isolated from hot ______ sediments near hydrothermal vents.
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Archaeoglobus couples the oxidation of H2, lactate, pyruvate, glucose, or complex organic compounds to the reduction of ______ to H2S.
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Ferroglobus is related to Archaeoglobus but is not a ______ reducer.
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Study Notes
Diversity of Archaea
- Archaea domain consists of several phyla, including Euryarchaeota, Crenarchaeota, Thaumarchaeota, Korarchaeota, and Nanoarchaeota.
- The exact ancestry of these groups remains a contentious issue, and phylogenetic trees constructed from 16S ribosomal RNA gene sequences often conflict with those made using other genomic locations.
- Archaea share common features such as ether-linked lipids, lack of peptidoglycan in cell walls, and structurally complex RNA polymerases, which resemble those of Eukarya.
- Archaea show enormous phenotypic diversity, with species carrying out chemoorganotrophic or chemolithotrophic metabolisms, and both aerobic and anaerobic species are common.
Metabolic Features of Archaea
- Chemoorganotrophy is widespread among Archaea, with fermentations and anaerobic respirations being common.
- Chemolithotrophy is also well established in the Archaea, with H2 being a common electron donor.
- Anaerobic respiration, especially forms employing elemental sulfur (S0) as an electron acceptor, is prevalent among the Archaea, especially Crenarchaeota.
- Aerobic respiration occurs widely in Thaumarchaeota and is common among a few groups of Euryarchaeota but is characteristic of only a few species of Crenarchaeota.
Euryarchaeota
- Euryarchaeota comprise a large and physiologically diverse group of Archaea.
- This phylum includes methanogens as well as many genera of extremely halophilic (salt-loving) Archaea.
- Methanogens are the strictest of anaerobes while extreme halophiles are primarily obligate aerobes.
Extremely Halophilic Archaea (Haloarchaea)
- Extremely halophilic Archaea inhabit environments high in salt, such as solar salt evaporation ponds and salt lakes, and artificial saline habitats.
- These organisms require very high salt concentrations, often near saturation, for growth.
- Key genera include Halobacterium, Haloferax, and Natronobacterium.
Methanogenic Archaea
- Methanogens are microorganisms that produce methane (CH4) as an integral part of their energy metabolism (methanogenesis).
- Methanogenesis is the terminal step in the biodegradation of organic matter in many anoxic habitats in nature.
- Key genera include Methanobacterium, Methanocaldococcus, and Methanosarcina.
- Methanogens show a diversity of morphologies and cell wall chemistries.
- Physiologically, methanogens are obligate anaerobes, and strict anoxic techniques are necessary to culture them.
- Substrates converted to CH4 by methanogens include CO2-type substrates, methylated substrates, and acetate.
Thermoplasmatales
- Thermoplasmatales are a phylogenetically distinct line of Archaea that contain thermophilic and extremely acidophilic genera.
- Key genera include Thermoplasma, Picrophilus, and Ferroplasma.
- These prokaryotes are among the most acidophilic of all known microorganisms, with Picrophilus being capable of growth even below pH 0.
- Most are thermophilic as well.
- Species of Thermoplasma are facultative aerobes, growing either aerobically or anaerobically by sulfur respiration.
Archaeoglobales
- Archaeoglobales are a group of Archaea that includes Archaeoglobus and Ferroglobus.
- Archaeoglobus was isolated from hot marine sediments near hydrothermal vents and couples the oxidation of H2, lactate, pyruvate, glucose, or complex organic compounds to the reduction of SO42− to H2S.
- Ferroglobus is related to Archaeoglobus but is not a sulfate reducer.
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Description
This quiz covers the diversity of Archaea, a domain of microorganisms, and their phylogenetic relationships, including phyla such as Euryarchaeota and Crenarchaeota.
