Archaebacteria

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.

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.

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.