Archaebacteria – Definition, Types, Characteristics & Examples
These archaebacteria are special since they live in some of the most harsh habitats such as extreme salty areas (halophiles), hot springs (thermoacidophiles) and marshy areas (methanogens).
Archaebacteria differ from other bacteria in having a different cell wall structure and this feature is responsible for their survival in extreme conditions. The cell membrane contains branched chain lipids (phytanyl side chains) which decreases membrane fluidity.
Archaebacteria have introns in their genetic sequence.
Archaebacteria are divided into three groups- methanogens, halophiles and thermoacidophiles.
(i) Methanogens : These bacteria are of marshy habitats. They are capable of converting CO2, methanol and formic acid into methane so named methanogens. These methanogens are present in the guts of several ruminant animals such as cows and buffaloes and they are responsible for the production of methane (biogas) from the dung of these animals. These are chemoautotrophs. Examples : Methanococcus, Methanobacterium etc.
(ii) Halophiles: These bacteria live in extreme saline environment such as salt lakes, sea, brines etc. In strong light, these halophiles develop a pigmented membrane (purple membrane) composed of a pigment called bacterio-rhodopsin (related to the one found in our Own eyes) to harness the sun s energy. The light energy is utilised to carry on ATP production but they cannot use this ATP in food synthesis. Hence, they are heterotrophs. Examples: Halobacterium and Halococcus.
(iii) Thermoacidophiles : These are capable of tolerating high temperature as well as high acidity and hence, the name thermoacidophiles. They often live in hot water springs where the temperature is as high as 80°C and the pH as low as 2. They oxidise sulphur to sulphuric acid under aerobic conditions and the energy obtained in this reactionIs utilised tor the synthesis of organic food. Hence, these are chemosynthetic in nature. The medium becomes highly acidic due to the production of sulphuric acid. Under anaerobic conditions sulphur is reduced to H,s. Examples: Thermoplasma, Thermoproreus ec.