Archaebacteria
living organisms
into large groups called kingdoms.
Five– Monera, Protista, Fungi, Plantae and Animalia
In 1996 scientists
decided to split Monera into two groups –
Archae and Eubacteria.
2 groups of baceteria were different in
many ways -Domain.
There are 3
Domains – Bacteria, Archea and Eukaryota
Greek; Archaio=ancient, bakterion=a small rod
.Arches are the first cells that originated
On the earth.
On the earth.
Prokaryotic
unicellular
spherical,
rod-shaped, spiral or irregular shape.
They range in
their size from 0.1 to over 15µ (microns) in length.
Nutritionally they
are chemolithotrophs or oganotrophs.
The cell wall do
not contain peptide glycan (muramic acid + D – amino acids)
but a range of other unique polysaccharides
are present.
The 16 µ r RNA
molecules differ greatly from other bacterial and eukaryotes.
The ribosomes of these
organisms are insensitive to chloramphenicol (antibiotic)
The first amino
acid to initiate the new polypeptide chain is methionine, instead of N-formyl methionine.
Habitat
They usually prefer extreme aquatic or
terrestrial habitats.
They are often
present in anaerobic, hypersaline , or high-temperature environments.
A few are symbionts in animal digestive systems
Morphology:
Archea are diverse in morphology. They
may be spherical, spiral, lobed or pleomorphic. Some are single celled, whereas other form filaments or aggregates.
They range in diameter from 0.1 to 15 micrometres.
Morphology:
Archea are diverse in morphology. They
may be spherical, spiral, lobed or pleomorphic. Some are single celled, whereas other form filaments or aggregates.
They range in diameter from 0.1 to 15 micrometres.
Cell walls
either Gram
positive or Gram negative.
differ from Eubacteria.
They donot have muramic acid and D-amino acids
-characteristic of eubacterial peptidoglycan.
All archaebacteria resist attact by lysozyme and B- lactam antibiotics such as penicillin
Cell walls
Methanobacterium and some other methanogens -pseudomurein, a peptidoglycan like polymer thas has L –amino acids in its cross-like , N-acetyltalosaminuronic acid instead of
N-acetylmuramic acid.
Gram negative archaeobacteria have a layer of
protein or glycoprotein outside their plasma membrane.
Membranes
lacks
fatty acids and instead have carbon moieties bonded to glycerol by ether
(instead of ester) linkages.
They contain polar
lipids such as phospholipids, sulfolipids and glycolipids and non-polar lipids
which are derivatives of the isoprenoid compound sqalene.
In spite of their
chemical uniqueness, membranes of most archaebacteria are structurally arranged
to form a typical bilayer like eubacterial
The presence of
ether linked lipids is such a unique characteristic of archaebacteria -used as a
biomarker for detecting archaebacteria in paleontological studies of rocks, sediment cores and
other fossil materials.
Genomes
The genome of archaebacteria consists of a
single covalently closed circular DNA molecule much smaller than that of eubacteria.
Plasmids of different sizes have been reported
from several bacterial.
The 16 µ r RNA molecules differ greatly from
other bacterial and eukaryotes.
The first amino acid to initiate the new
polypeptide chain is methionine, instead of N-formyl methionine
The ribosomes of eubacterial are sensitive to Chloramphenicol while the archaebacteria are not.
The
diphtheria toxin affects archaebacterial but not eubacteria. Both these inhibitors affect the translational process in
the cell.
Classification
Three distinct
groups
the methanogens,
extreme halophiles
extreme thermophiles
The Methanogens
They are strictly
obligate anaerobes.
While producing methane they utilize electrons
generated by oxidation of hydrogen or simple organic compounds such as acetate
and methanol.
The habitats like
marshes, swamps, pond and lake mud,
the intestinal
tract of humans and animal,
the rumen of cattle and
anaerobic sludge digester in sewage treatment
systems are ideal for these archaebacteria.
Ex- Methanobacterium, Methanospirillum, Methanococcus.
Extreme Halophiles (Halobacteria)
They are obligate halophiles found in salt
lakes, the Dead sea, foods preserved by salting and salt production industrial
plants.
They grow in salt
with concentrations above 15 %.
They are aerobic.
They stain Gram
negative and range from rod or disc-shaped cells (Halobacterium) to cocci (Halococcus).
Extreme Halophiles (Halobacteria)
The colonies are
red to orange colour due to presence of carotenoids which seem to protect the cells against the damaging effect
of sunlight.
There mechanism of
photo production of energy is unique as they use bacteriorhodopsin, a special pigment, as
photoreceptor.
Ex. – Halobacterium, Halococcus.
Extreme Thermophiles (Hyperthermophiles)
They are gram
negative and anaerobic, characterized by a remarkable ability to grow under
high acidic conditions at high temperature.
They are Gram
negative and anaerobic. Some can survive at near boiling point of water.
Ex. Sulfobolus, Pyrodictium, Thermoplasma
Some of the differences between Archea and other organisms:
1. Archea bacterial cell wall is made up of pseudo peptidoglycon instead of peptidoglycon.
2. Ether linked lipids are present in Archeabacterial cell membrane whereas ester linked lipids in eubacteria.
3. Archeabacteria has single DNA polymerase whereas eubacteria has three DNA polymerases
4. Archea tRNA lacks thymine, instead 1-methyl pseudo uridine is present.
Some of the differences between Archea and other organisms:
1. Archea bacterial cell wall is made up of pseudo peptidoglycon instead of peptidoglycon.
2. Ether linked lipids are present in Archeabacterial cell membrane whereas ester linked lipids in eubacteria.
3. Archeabacteria has single DNA polymerase whereas eubacteria has three DNA polymerases
4. Archea tRNA lacks thymine, instead 1-methyl pseudo uridine is present.
