Fungi Cell Wall And Archaea Cell Wall: 5 Important Facts

Fungi are heterotrophic saprophytes and depend upon autotrophic plants for their food and nutrition. While archea belongs to the class of bacteria that can survive in extreme conditions like hot springs to super cold mountains, we can also call them extremophiles.

The fungal cell wall is majorly formed by polymeric long, a branched chain of two polysaccharides, N-acetyl glucosamine(NAG) and N-acetyl muramic acid(NAM) respectively. While archaeal cell wall is purely proteins with the exception of pseudopeptidoglycan in methanogens.

Do both archaea and fungi have cell walls?

The archaeal cell wall helps to create a physical barrier between the cytosol & outer surrounding and it also prevents them from heat, acidity, salinity and other environmental factors. The cell wall of fungi also protects the cell from viral and bacterial virulence, osmotic stress, and ionic exchange and facilitates the absorption of nutrients from their autotrophic host.

Yes, they both possess a well-defined cell wall that maintains the definite shape and structure of the cell. The cell wall protects the cell from different pathogenicity and is responsible for the interaction and transportation of molecules with the environment. They also determine cell shape and help to maintain the metabolism of the cell. Chitin is also found in exoskeletons of many animals like arthropods, crabs, shrimps, etc.

Structure of units of amino sugar found in fungal cell wall
Image credit: Wikimedia commons

Are fungi cell walls and archaea cell walls the same?

The fungal cell wall is the structure interconnected by a polymer of a derivative of chitin and α-β glucans results in the stiffness of the cell wall and fungal pathogenicity. Cell walls possess some specific protein which facilitates the adhesion of fungus to the substratum. Chitin is a fundamentally significant part of the fungal cell wall found nearest to the plasma layer. Archaeal cell wall contains S-layer but is devoid of peptidoglycans.

No, they both are chemically distinct. They show different features in their composition based on (1) chirality of glycerol, (2) ether linkage, (3) isoprenoid chains, and (4) branching of side chains. Cell wall components are helpful in 10% of cellular protein synthesis. All archaeans can oxidise pyruvate into acetyl CoA. Some archebacteria need cell walls as their plasma layer contains a mannose-rich glycoprotein and a lipoglycan.

Methanogens lack pyruvic dehydrogenase and are unable to perform the tri-carboxylic acid cycle. The cell wall of archaeans is made up of pseudomurein, methanochondroitin, glutaminylglycan, sulfated heteropolysaccharides and a multilayer sheath of proteins. They are having branched chain of hydrocarbons attached to glycerol by ether (rather than an ester) linkages. Thermophilic archaea sometimes link two glycerol groups to form long tetraethers. Diether side chains are usually 20 carbons long, and tetra-ether chains contain 40 carbon atoms. However, cells can adjust chain lengths by cyclizing the chains to form pentacyclic rings.

Difference between archaea and fungi cell walls

The cell wall composition of fungi is mannan, arabinan, and chitosan cross-linked with  α-1,3 glucan and β-1,6 glucan linkages. Many fungal cell walls also secret melanin to reduce phagocytosis, and susceptibility to antifungal drugs and also alter the cytokinins response. In each organism of monera, protista and fungi, the cell wall behaves as the first line of defence from biotic and abiotic attacks.

The main difference between the archaeal cell wall and the fungal cell wall is the lack of peptidoglycan in archea while fungi possess peptidoglycan(also known as murein) or units of amino sugar i.e. Chitin is a strong but flexible nitrogen-containing polysaccharide consisting of N-acetylglucosamine residues. Archea is made out of glycerol-ether lipids, whereas bacteria and other eukaryotic organisms have membranes composed mainly of glycerol-ester lipids.

File:Figure 22 02 07f.jpg - Wikimedia Commons
Difference between glycerol-ether and glycerol-ester bond in Domain Archea and Domain Eucarya.
Image credit: Wikimedia commons

So, the constituents of most of the archaebacteria are different from fungi. Enzymes present in the fungal cell wall are glucan synthase, chitin synthase, and mitogen-activated kinase aids in the alteration of gene expression and leads to the formation of a modified cell wall. Unlike archea, the fungal cell wall is more elastic and flexible to prevent the cell from osmotic stress.

Similarities between fungi cell walls and archaea cell walls

Like some other prokaryotes, fungi can digest insoluble organic matter by secreting exoenzymes, then absorbing the solubilized nutrients by the process known as osmotrophy. They also can reproduce through asexual spores and sexually by gametangia. Both fungi and archea are cosmopolitan and often colonial. Like bacteria, some fungi are also unicellular like yeast.

As fungi, some archaebacteria are also saprophytic though dependent upon the dead and decaying organic matter as a source of carbon, nitrogen, phosphorus, and other critical constituents for their survival. They both can act as a pathogen for plants and animals. They both are chemoorganoheterotrophs as they play a vital role in the biogeochemical cycling of organic matter.

Archaebacteria and fungi are lying from two different domains i.e. Domain Archea and Domain Eucarya but still show some similarities based on molecular machinery. As per the DNA sequence data, lateral gene transfer occurred repeatedly throughout evolution and Eucarya have some genes which correlate with the bacterial origin which means they may share very similar genes. These features can be depicted in the table given below:

fungi cell wall and archaea cell wall
Similar features in Archea and Eucarya

They contain many rare lipids with repetitive isoprenyl groups attached to glycerol and an S-layer of glycoproteins in a grid-like arrangement attached to the membrane. So, the Surface layer glycoprotein is the most characteristic glycoprotein of archaea.

To date, mainly two hydrolytic enzymes are discovered in archea and are endoisopeptidasees- PeiW & PeiP from Methanothermobacter wolfeii. They also produce glycoproteins, exotoxins and some glycan binding proteins.

There is membranous protein i.e. Membrane translocase which transfers the MurNAc pentapeptide to undecaprenyl (C55) phosphate (also known as bactoprenol phosphate) inside the membrane. This lipid is similar to the eukaryotic dolichol carrier used in N-glycan synthesis. The final product, called Lipid I, contains a pyrroline acid bond.

Due to the absence of peptidoglycan, the cell wall of archaebacteria is harder to degrade as very few enzymes can act upon it. They possess no target proteins for antibiotics to break down the cell wall.

While the fungal cell wall is made up of peptidoglycan, chitin and chitosan. Chitosan is the derivative form of chitin as they are deacetylated chitin. After cellulose and lignin, it is the most abundant and natural polymer. The molecular weight of both chitin and chitosan is more than 105 Dalton and is insoluble in water, having antimicrobial activity.

Conclusion

Archea and Fungi may be similar in molecular response that is they may share common genes that have given similar expressions but they varied from each other on the phenotypical ground. They showed structural diversity. The major constituent of the cell wall of fungi is chitin and a derivative analogue of chitin that is chitosan while the archaeal cell wall is made up of glycoconjugates and polysaccharides.

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