Difference between Pili and Fimbria

Pili and fimbriae are the terms used to describe short, hair-like projections on the surface of prokaryotic cells such as bacterial cells, etc. Pili and fimbriae are the distinct projections of the cell’s flagella, and are used by the cell to anchor itself to the surface or for fixation. These pili and fimbriae are present on the cell surface. The key difference between pili and fimbriae is that pili are found in gram-negative bacteria, while fimbriae are found in gram-negative and gram-positive bacteria. The other important differences between pili and fimbria are in size, length, and diameter, and pili can also be used in sexual reproduction; These pili are called sexual pili.

Comparative chart

What is Pili?

Pili are the projections or appendages present on the cell surface of the cell. They are present in gram-negative bacteria. Pili are elongated, thick and tubular in structure. They are made up of a special protein known as pilin, which is why they are called Pili. Pili have a very rigid structure and are governed by plasmid genes. The pili are mainly used for the attachment of the cell with the other surface, but indirectly, they are also used in the sexual reproduction of the cell. Therefore, they are also used in the reproduction of cells; such pili are known as sexual pili. Sex pili are useful for sharing genes between the two cells. Pili also has receptors for many viruses. Pili are found abundantly in the cell compared to other structures. Note that they have no role in cellular locomotion. They are present inNeisseria gonorrhoeae, where they are used for fixation in the urogenital and cervical epithelium in case of disease.

Fimbriae are the projections found in gram negative and gram positive bacteria. They are shorter in structure and have a thin diameter. Fimbriae are so named because they have fibrillin protein in their structure. Fimbriae have a less rigid structure and are governed by genes from bacteria in the nucleus. The fimbriae are specialized structures that have the sole function of attachment. They have no function in cellular locomotion. They have no receptors on them and form clumps of cells while sticking to other surfaces or to each other. An example of fimbriae is Shigella dysenteriae, where it is used to adhere to the surface of the intestine to produce toxic substances that mostly cause diarrhea.

Pili vs. Fimbrias

• Pili are present in gram-negative bacteria, while fimbriae are found in both gram-negative and gram-positive bacteria.
• Pili are larger in size and thicker in diameter, while fimbriae are smaller in size and thinner in diameter.
• Pili have a very rigid structure, and plasmid genes govern them, on the other hand, fimbriae have a less rigid structure and are governed by bacteria genes in the nucleus.
• Pili have receptors for many viruses, whereas fimbriae have no receptors.
• Pili are made up of a special protein known as pilin, which is why the name pili is used, and conversely, fimbriae have fibrillin protein in their body.