1. The Archaea 1 20 Copyright © McGraw-Hill Global Education Holdings, LLC. Permission required for reproduction or display.

2. 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 2

3. 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 CO 2 fixation, and the ability of some to synthesize methane 3

4. Archaeal Taxonomy Five major physiological and morphological groups 4

5. 5 General Groups Consists of many classes, orders, and families –methanogens –halobacteria –thermoplasms –extremely thermophilic S 0 -metabolizers –sulfate-reducers 5

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7. 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 7

8. 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 8

9. 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 9