CELL WALL OF ARCHAEA

 CELL WALL OF ARCHAEA

·       The cell wall is present in most archaea except Thermoplasma and Ferroplasma.

·       The cell wall of Archaea is surrounding the cell outside the cytoplasmic membrane and is mediating the interaction with the environment.

·       Archaeal cell wall can be involved in Cell shape maintenance, Protection against Virus, Heat, Acidity or Alkalinity.

·       Archaea do not have Peptidoglycan but have Pseudomurein and different in its composition to Murein.

·  Archaea have Pseudopeptidoglycan and it is similar to bacterial peptidoglycan (morphologically, functionally) but is chemically distinct.

·       In Archaea, instead of NAM, it contains N-Acetyltalosamine Uronic Acid (NAT) linked to NAG, with peptide interbridges to increase strength.

·  In some Archaea, the Cell wall is composed of Glycan polymers like Glutaminylglycan, Heterosaccharide, Methanochondroitin or Pseudomurein, which can be further supported by an S-layer.

·       Many Archaea possess a Protein or Glycoprotein Surface layer (S-layer) as their sole cell wall structure.

·    S-layer consists of hexagonal patterns of protein or glycoprotein that self-assemble into a crystalline lattice 5 to 25 nm thick.

·       The role of the S-layer or cell wall in archaea is for physical and chemical protection.

·      Methanochondroitin is a cell wall polymer found in some archaeal cells, similar in composition to the connective tissue component chondroitin, found in vertebrates.

Difference between Gram positive bacterial cell wall, Gram negative bacterial cell wall and Archaea cell wall

Features	Gram Positive Bacterial Cell wall	Gram Negative Bacterial Cell wall	Archaea Cell wall
Gram staining	Appears in Violet colour	Appears in Pink colour	Not applicable
Thickness	15 – 18 nm	7 – 8 nm	20 – 40 nm
Peptidoglycan	Thick (Multilayered)	Thin (Single layered)	Similar to peptidoglycan, a Polysaccharide called Pseudomurein is present Cell walls of some Archaea lack Pseudomurein and instead contain polymers of glucose, glucuronic acid, galactosamine uronic acid, and acetate. It also contains Proteins or Glycoproteins.
Teichoic acids	Present	Absent	Absent
Periplasmic space	Absent	Present	Absent
Outer membrane	Absent	Present	Absent
Lipopolysaccharides	Low	High	Absent
Lipid & Lipoproteins	Low (Only in Acid fast bacteria have lipid linked to Peptidoglycan)	High (because of the presence of Outer membrane)	Low
Porins	Absent	Present	Absent
Cell wall disruption by Lysozymes	High (After digestion of peptidoglycan layer, Gram positive bacteria become Protoplast)	Low (After digestion of peptidoglycan layer, Gram   negative bacteria become Spheroplast)	Resistant to Lysozyme
Rigidity and Elasticity	High rigid & Less elastic	Less rigid & High elastic	Semi-rigid and Less elastic
NAG	Present	Present	Present
Presence of NAM	Present	Present	NAM is absent and replaced by N-Acetyltalosamine Uronic Acid (NAT)
Glycosidic linkage	β-1,4 glycosidic linkage	β-1,4 glycosidic linkage	β-1,3 glycosidic linkage
Pseudo-crystalline Proteinaceous Surface Layer (S - layer)	Absent	Absent	The most common cell wall among archaeal species is a surface layer called the S-layer.
Methanochondrotin (cell wall polymer)	Absent	Absent	Present
Protein sheaths	Absent	Absent	Present
Sensitivity to Penicillin	Sensitive	Resistant	Resistant