Archaebacteria (Archae—ancient; bact—rod) 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).
The characteristics of this domain are
(i) They are most primitive prokaryotes.
(ii) They are found in stressed environment conditions,
such as high salt content (Great Salt Lake, The Dead
Sea), edge of the ocean, hot sulphur springs, volcanic
walls, gut of animals, etc.
(iii) Their cell walls lack peptidoglycan. In most cass,
the cell wall is composed of non-cellulosic
polysaccharides and some proteins.
In some
members, cell wall may even be absent. This feature
of having different kinds of cell walls is responsible
for their survival in extreme conditions.
(iv) Most of the archaebacteria are chemoautotrophs.
orrophs.
Types of Archaebacteria
Archaebacteria are of following three types
i. Methanogens
These are strictly anaerobes. They live anaerobically in gut
of several ruminants such as cows, buffaloes, goats, etc.
These bacteria have been exploited for the production of
methane gobar gas from the dung of these animals. These
bacteria also help in fermentation of cellulose. They
produce almost 65% of atmospheric methane.
Examples are Methanobacterium, Methanobacillus,
Methanosarcina and Methanococcus.
Knowledge Plus
• Methane is a gy.)liutant that contributes to greenhouse effect
and global warming.
• The fermentation of cattle dung by methanogens is done
in sgmlally designed gobar gas plants to prcriuce cmklng gas
ii. Halophiles
These are found in extremely saline environments like salt
lakes, salt marshes, salt pans, salt solutions, etc. They are
mostly anaerobes. They contain a chemical called
halorhodopsin to pump in chlorides into the cell to pr0ent
cellular dehydration.
Halobacterium develops purple membrane having
photoreceptor pigment bacteriorhodopsin. In light, it
acts as a proton pump and helps in synthesis of AT P.
The formation of ATP is a survival mechanism under
anaerobic conditions.
Examples include Halobacterium and Halococcus.
iii. Thermoacidophiles
These archaebacteria can live in both extreme heat and
acidic pH (around 2) environment conditions. Under
anaerobic conditions, these organisms oxidise sulphur to
sulphuric acid.
2S+ 2H20+ 302 2H2S04 + Energy
Thermoacidophiles can survive in high temperature and
low pH conditions because of the following special
features
(a) Special branched chain lipids in cell membranes
that reduce cell fluidity.
(b) Enzymes that can work at low PH.
(c) Enzymes that are resistant to high temperature
coagulation. Examples
are Sulfbbolus,
Thermoplasma and Thermoproteus.
Importance of Archaebacteria
Archaebacteria can live in extreme environments, so
they are useful in
(i) Modern biotechnology
(ii) Generation of biogas
(iii) Thermophilic enzymes
(iv) Biosensors
(v) Restriction enzymes, etc.