Fimbriae vs Pili

What is Fimbriae?

  • Fimbriae and pili are filamentous structures composed of protein that extend from the surface of a cell and can have many functions.
  • Fimbriae are short, thin, hair-like performances that are thinner than flagella and should not participate in the movement.
  • A cell that can be covered with up to 1000 fimbriae.
  • They are only visible under an electron microscope due to their small size.
  • These are thin tubes consisting of helically arranged protein subunits, with a diameter of 3 to 10 nm and a length of up to several micrometers.

What is Pili?

  • Pili are similar to fimbriae but are typically longer.
  • Only one or a few pili are present on the surface of a cell.
  • Because pili can be receptors on certain types of viruses, they can be seen under a microscope where they are coated with particles.
  • Many classes of pili are known, distinguished by their structure and function.

Similarities Between Fimbriae and Pili

  1. Both the fimbriae as well as pili are filamentous in structure.
  2. Both fimbriae and pili are attached with the bacterial cell surfaces.
  3. Both are made up of proteins but these proteins may be different.

Difference Between Fimbriae and Pili

fimbriae vs pili, difference between fimbriae and pili
StructureFimbriae are tiny, bristle-like structurePili are hair like, and tubular in structure
PresencePresent in both gram positive and gram negative bacteriaPresent only in gram negative bacteria
Protein CompositionComposed of Fimbrillin protein.Composed of Pilin protein.
LengthFimbriae are shorter as compared to piliPili are longer as compared to fimbriae
DiameterThey are thinner than piliThey are thicker than fimbriae
Number/Cell200-400 fimbriae/cell1-10 pili/cell
RigidityFimbriae are less rigid than piliPili are more rigid than fimbriae
Administered byFimbriae are administrated by bacterial genes in the nucleoid area.Pili are administrated by plasmid genes.
Role in AttachmentPlay important role in attaching the cellsDo not take part in cell attachment
Role in ConjugationThey do not take part in cell conjugationThey play important role in cell conjugation
Role in MotilityDo not function as a motilitySome pili take part in motility. i.e. Type IV pili
Main FunctionMain function of fimbriae is attachment of cell surfaceMain function of pili is conjugation of cells
ExamplesSalmonella typhimurium, Shigella dysenteriae.Neisseria gonorrhoeae

References and Sources

Further Readings

  1. Bacterial Flagella, Fimbriae and Pili, Capsule
  2. Fimbriae vs Flagella
  3. Instruments used in Microbiology Laboratory
  4. Algae – Definition, Classification, and Examples
  5. Bacterial Growth and Nutrition
  6. Serial Dilution in Microbiology
  7. Negative Staining
  8. Types of Extremophiles
  9. Extremophiles
  10. Nutritional Requirements of Micro-Organisms