Archaebacteria - Types

Description:

Archaebacteria are of three types – methanogens, halophilic and thermoacidophilic. Methanogens and halophiles are placed in the division euryarchaeota while thermoacidophiles are include in division creuarchaeota.

Methanogens

• Strictly anaerobes.

• Autotrophic bacteria and obtain energy and carbon from decomposition products.

• Occur in marshy areas where they convert formic acid and carbon dioxide into methane with the help of hydrogen. This capability is commercially used in the production of methane and fuel inside gas plants.

• Some methanogen archaebacteria live as symbiont inside the rumen in the stomach of herbivorous animals.

• Help in the fermentation of cellulose.

Halophiles

• Named because they usually occur in salt rich substrata.

• Aerobic chemoheterotrophs.

• Cell membranes have red carotenoid pigment for protection against harmful solar radiations.

Halophiles can tolerate high salt concentrations due to −

• Presence of special lipid in the cell membranes.

• Occurrence of mucilage covering.

• Absence of sap vacuoles and hence plasmolysis is also absent.

• High internal salt content.

Thermoacidophiles

• Have dual ability to tolerate high temperature as well as high acidity.

• They often live in hot sulphur springs where the temperatures may be as high as 80 O C and pH as low as 2.

• They are chemosynthetic and obtain energy for synthesis of food from oxidizing sulphur.

Thermoacidophiles are able to tolerate high temperature as well as high acidity due to −

• Branched chain lipids in the cell membranes.

• Presence of special resistant enzymes capable of operating under acidic conditions.