Diversity of Archaea (Lec 15)

Methanogenesis and Archaea

• Only the domain Archaea can perform methanogenesis.
• The major group of Archaea that includes extremely halophilic organisms is Halobacteriales.
• The major group of Archaea that inhabits extreme heat or cold environments is Thermococci.
• The common characteristic of all Archaea is the presence of ether lipids in their membranes.

Haloarchaea

• Haloarchaea require high salt concentrations for survival.
• The primary habitat of haloarchaea is salt lakes and salt mines.

Thermophilic Archaea

• Thermoplasmatales are found in the major group of Archaea called Thermococci.
• Methanogens are found in the major group of Archaea called Euryarchaeota.
• Desulfurococcus is a type of thermophilic archaeon that can grow in temperatures above 90°C.

Pyrolobus fumarii

• The optimum growth temperature for Pyrolobus fumarii is around 100°C.

Ignicoccus

• Ignicoccus is a type of archaeon that lacks a cell wall.
• The outer membrane of Ignicoccus is similar to that of Gram-negative bacteria.
• Ignicoccus is not able to perform methanogenesis.

Hyperthermophiles

• The upper temperature limit for survival without growth for microbial life is around 122°C.
• Hyperthermophiles use ether lipids as a molecular adaptation for life at high temperatures.
• The major chaperonin protein complex in Pyrodictium is the thermosome.
• Reverse gyrase is an enzyme that introduces positive supercoils into DNA and stabilizes DNA only in hyperthermophiles.
• Chaperone proteins refold partially denatured proteins in hyperthermophiles.

Taq Polymerase

• Taq polymerase is a thermostable DNA polymerase from the thermophilic archaeon Thermus aquaticus.

Archaeal Groups

• Euryarchaeota is the group of Archaea that includes methanogens, halophiles, and thermophiles.
• Thermococci is the group of Archaea that is known for its thermophilic and acidophilic characteristics.
• Pyrodictia is the group of Archaea that is commonly found in submarine or terrestrial volcanic habitats.
• Sulfolobus is the group of Archaea that is known for its ability to oxidize reduced sulfur or iron in acidic hot springs.

High-Temperature Environments

• The environment most likely to harbor extremely halophilic Archaea is salt lakes and salt mines.
• The environment most likely to harbor the most thermophilic Archaea is deep-sea hydrothermal vents.

Microorganisms

• Pyrolobus fumarii has the highest temperature resistance among all microorganisms.
• There is no upper limit for microbial life, and it is plausible that microorganisms can survive in extremely high-temperature environments.