CELL WALL APPENDAGES: THE GLYCOCALYX

 

Appendages literally means “Parts of the body that protrude out from the main body”. Glycocalyx, fimbriae, pili, flagella and S-layer are the main cell wall appendages of prokaryotes. Glycocalyx is found on the outer surface of the cell wall of prokaryotes (mainly bacteria).

There are two types of Glycocalyx based on their structure and adherence to the bacterial cell wall, namely:

1. Capsule
2. Slime layer

Capsule

When glycocalyx is tightly bound to the cell wall of bacteria, it is referred to as capsule. It is gelatinous in nature and cannot be easily stained and removed from the bacterial cell wall

Slime Layer

The glycocalyx called “slime layer” is loosely bound to the cell wall of bacteria. Slime layer is irregular and can easily be removed via centrifugation from the bacterial cell wall.

Composition and structure of Glycocalyx

Capsule is made up of polysaccharide. It contains polypeptides in some cases. e.g D-glutamic acid in B. anthracis. The structure of bacterial capsule can be viewed under the microscope by using India ink staining technique while slime layer majorly consist of polysaccharides, glycoproteins, and glycolipids.

Functions of Glycocalyx

• Disease: It is a virulence factor in most bacteria, and it contributes to their ability to cause diseases in their host.
• Protection: Glycocalyx protects bacteria from antibiotics, chemicals and against the lytic and phagocytic activities of host’s white blood cells.
• Adherence to surfaces: The sticky nature of the glycocalyx enables bacteria to attach themselves firmly to the surface of their host. Streptococcus mutans, the causal agent of tooth decay adheres to the surface of decaying teeth with the help of glycocalyx.
• Avoidance of desiccation: Glycocalyx (especially capsule) contains water as its constituent. This help to prevent dryness of the bacterial cell.
• In cell-cell recognition: The glycocalyx carries receptors on their surface that allows them to bind to other cells of close species.

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