Capsule vs. Glycocalyx — What's the Difference?

The bacterial capsule is a distinct, gelatinous layer that envelops the cell wall, providing a barrier against phagocytosis and environmental stresses, such as dehydration or antibiotic action. It is particularly important in pathogenic bacteria, enhancing their ability to cause disease by preventing detection and destruction by the host's immune system. In contrast, the glycocalyx is a more generalized term referring to the extracellular polymeric material covering cell surfaces. In bacteria, it can include the capsule when present, but in eukaryotic cells, the glycocalyx consists of glycoproteins and glycolipids that contribute to cell-cell recognition, adhesion, and protection.

Capsules are composed primarily of polysaccharides, but can sometimes contain polypeptides, and their production is often associated with pathogenic bacteria. The glycocalyx, however, is made up of a variety of molecules, including carbohydrates, proteins, and lipids, contributing to a diverse range of functions beyond protection, such as cell communication and the immune response.

In terms of function, the bacterial capsule is specifically adapted for protection and evasion within the context of a host-pathogen interaction, making it a key factor in the virulence of pathogenic bacteria. The glycocalyx's functions are broader, encompassing cell recognition, adhesion (such as in the formation of biofilms by bacteria), and protection in a wide array of biological contexts, including but not limited to pathogenesis.

While the capsule is a feature that is not present in all bacteria and is mostly associated with pathogenic strains, the glycocalyx is a ubiquitous feature of all cells, highlighting its fundamental role in cell biology across both prokaryotes and eukaryotes.