1

The Archaea

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

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 CO2 fixation, and the ability of some to synthesize methane

4

Archaeal Taxonomy• Five major physiological and morphological groups

5

5 General Groups• Consists of many classes, orders, and

families– methanogens

– halobacteria

– thermoplasms

– extremely thermophilic S0-metabolizers

– sulfate-reducers

6

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

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

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