What They Look Like?
What They Eat?
Where They’re Found?
How They’re Different?
New branch of life….
In 1970s carl woese proposed -3 domain classification
Based on sequencing of 16s r RNA
The organism he revealed-the achea..
Classifying Archaea remains difficult, majority of these organisms have never been studied in the laboratory and have only been detected by analysis of their nucleic acids in environmental samples.- ( metagenomics)
Archaea are more wounderful than you know…!
Introduction to the Archaea
Stain either Gram +ve or Gram –ve
Shapes – Spherical, rod, spiral, lobed, irregularly shaped or pleomorphic
Single cells or filaments or aggregates, diameter from 0.1 to over 15 μm
Multiplication – binary fission, budding, fragmentation or other unknown mechanisms
A postage-stamp like sheet of the square cells of Halquadratum walsbyi.
Aerobic, facultative and strictly anaerobic
Range from chemolithotrophs to organotrophs
Mesophilic & hyperthermophiles
Found in extreme environments
Few are symbionts in animal digestive system eg- the marine archaean Cenarchaeum symbiosum lives within (is an endosymbiont of) the sponge Axinella mexicana.
Archaeal cell envelopes
One of he distinctive feature of the archaea is the nature of envelope
S-layer is the major component of the cellwall
Some archaea lacks cellwall but have a glyocalyx lying out side the cell membrane
Capsules and slime layers are rare among archaea
Archaeal cell walls
Archael cellwall lacks peptidoglycan and exhibit considerable variety in terms of their chemical make up
The most common type of archaeal cell wall is an S-layer composed of either protein or glycoprotein the layer may be as thick as 20 to 40 nm. eg; methanococcus, halobacterium
Other archaea have additional layers of material outside the S-layer methanospirillum has a protein sheath external to the s-layer
methanosarcina has a layer of chondroitin- like material, this material is called methanochondroitin
In some archaea S-layer is the outer most layer and seperated from the plasma membrane by pseudomurein pseudomurein is a peptidogycan-like molecule.
differs from pepidoglycan in that it has N-acetyltalosaminuronic acid instead of N-acetylmuramic acid ,and beta (1 3)glycosidic
linkage insted of beta (1 4) glycosidic linkage. eg- Methanobacterium, Methanothermus and Methanopyrus
The last type of archael cellwall does not include an s-layer .these archaea have a wall with a single, homogenous layer resembling in gram-positive bacteria
Archaeal Lipids & Membranes
Archaeal plasma membranes
Archaeal membranes are composed primerly of lipids that differ from bacterial and eukaryotic in two ways.
1. They contain hydrocarbons derived from isoprene units(five
2. Hydrocarbons attached to glycerol by ether linkage rather
than ester links