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20
The Archaea
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Archaea
• Many features in common with Eukarya and Bacteria
• Other elements are unique to Archaea
– unique rRNA gene structure
– capable of methanogenesis
• Highly diverse with respect to morphology,
physiology, reproduction, and ecology
• Best known for growth in anaerobic, hypersaline, pH
extremes, and high-temperature habitats
• Also found in marine arctic temperature and tropical
waters
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Archaeal Metabolism
• Great variation among the different archaeal
groups
• Organotrophy, autotrophy, and phototrophy
have been observed
• Differ from other groups in glucose
catabolism, pathways for CO2 fixation, and
the ability of some to synthesize methane
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Archaeal Taxonomy
• Five major physiological and morphological groups
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5 General Groups
• Consists of many classes, orders, and
families
– methanogens
– halobacteria
– thermoplasms
– extremely thermophilic S0-metabolizers
– sulfate-reducers
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Methanogens
• All methanogenic microbes are Archaea
– called methanogens: produce methane
• Methanogenesis
– last step in the degradation of organic
compounds
– occurs in anaerobic environments
• e.g., animal rumens
• e.g., anaerobic sludge digesters
• e.g., within anaerobic protozoa
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Ecological and Practical
Importance of Methanogens
• Important in wastewater treatment
• Can produce significant amounts of methane
– can be used as clean burning fuel and energy source
– is greenhouse gas and may contribute to global
warming
• Can oxidize iron
– contributes significantly to
corrosion of iron pipes
• Can form symbiotic relationships with certain
bacteria, assisting carbon/sulfur cycling
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Halobacteria
• Extreme halophiles (halobacteria)
– require at least 1.5 M NaCl, optimum 3-4 M
• cell wall disintegrates if [NaCl] < 1.5 M
• Aerobic, respiratory, chemoheterotrophs with
complex nutritional requirements
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