Pili and fimbriae are the terms that used to describe a short, hair-like projections on the surface of prokaryotic cells like bacterial cells, etc. Pili and fimbriae are the projections other than flagella of the cell, and they are used by the cell for anchoring itself with the surface or for attachment. These Pili and fimbriae are present at the cell surface. The key difference between pili and fimbriae is that pili are found in gram-negative bacteria, whereas fimbriae are found in Gram-negative as well as in gram-positive bacteria. The other prominent differences between pili and fimbriae are of size, length, and diameter, and pili may also be used in sexual reproduction, such pili are called sex pili.
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 long, thick and tubular structure. They are composed of a special protein known as pilin, due to which they are named Pili. Pili are very rigid structure, and plasmid genes govern them. Pili are mainly used for the attachment of the cell with the other surface but indirectly, they are also used in sexual reproduction by the cell. Hence, they are also used in the reproduction of cell; such pili are known as sex pili. Sex pili are useful in sharing genes between the two cells. Pili also have receptors for many viruses. Pili are abundantly found in the cell as compared to other structure. Note that they do not have any function in locomotion of cell. They are present in Neisseria gonorrhoeae, where they are used for attachment in urogenital and cervical epithelium in disease.
What is Fimbriae?
Fimbriae are the projections found in gram negative and gram positive bacteria. They are shorter structure, and they have a thin diameter. Fimbriae are so named because they have fibrillin protein in their structure. Fimbriae are less rigid structure and are governed by genes of bacteria in the nucleus. Fimbriae are specialized structures that have the only function of attachment. They do not have any function in locomotion of cell. They have no receptors on them, and they form clusters of cells while sticking with other surface or with each other. An example of fimbriae is Shigella dysenteriae, where it is used to attach on the surface of the intestine to produce toxic substances that mostly cause diarrhea.
Pili vs. Fimbriae
- Pili are present in gram-negative bacteria, whereas fimbriae are found both in 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 are very rigid structure, and plasmid genes govern them, on the other hand, fimbriae are less rigid structure and are governed by genes of bacteria in the nucleus.
- Pili have receptors for many viruses, whereas fimbriae have no receptors on them.
- Pili are composed of a special protein known as pilin, due to which name pili is used and contrary to that, fimbriae have fibrillin protein in their