Archaea Bacteria

Early Origins


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)

Carl woese

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.[180]

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 carbon, branched)

2. Hydrocarbons attached to glycerol by ether linkage rather than ester links

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