(a) Methanogens : (1) The archaebacteria are strict anaerobes. Nutritionally they are "autotrophs" which obtain both energy and carbon from decomposition products.
(2) They occur in marshy areas where they convert formic acid and carbon dioxide into methane. (3) This capability is commercially exploited in the production of methane and fuel gas inside gobar gas plants, e.g., Methatiobacterium, Methanococcus.
(b) Halophiles : (1) Halophiles are named so because they usually occur in salt rich subtrata like salt plant, and salt marshes e.g., Halobacterium, Halococcus. (2) They are aerobic chemoheterotrophs. Their cell membrane have red carotenoid pigment for protection against harmful solar radiations. (3) Halophiles are able to live under high salt conditions due to three reasons :
(i) Presence of special lipids in the cell membranes.
(ii) Occurence of mucilage covering.
(iii) Absence of sap vacuoles and hence plasmolysis.
(c) Thermoacidophiles : (1) These archaebacteria have
dual ability to tolerate high temparature as well as high acidity. (2) They often live in hot sulphur springs where the temperature may be as high as 80°C and pH as low as 2, e.g., Thermoplasma, thermoproteus. (3) These archaebacteria are chemosynthetic. (4) Under aerobic conditions they usually oxidise sulphur to sulphuric acid.
2S + 2H2O + 3O2 + 2H2SO4
(5) Thermoacidophiles are able to tolerate high temperature and high acidity due to two reasons :
(i) Branched chain lipids in the cell membranes.
(ii)Presence of special resistant enzymes capable of operating under acidic conditions.