Pilus- latin name for “Hair” is a hair-like cell wall appendage found on the surfaces of many prokaryotes (especially bacteria). Pili (plural of Pilus) is shorter and thinner than flagella (another important bacterial cell wall appendage).
The bacterial pilus is made up of fibrous protein sub unit called pilin used by bacteria for genetic transfer process called conjugation
The bacterial pili are of two types:
- Conjugative pili
- Type IV pili
During the horizontal gene transfer process called bacterial conjugation, extrachromosomal DNA called plasmid is transferred from the donor bacterium (F+) to the recipient bacterium (F–). This is done by cell to cell contact of implicated bacteria. The pili involved conjugation are usually called sex pili. Examples of bacteria that use conjugation as their mode of gene transfer are Bacillus sp., Enterococcus faecalis, Escherichia coli and Staphylococcus species
Type IV pili
Type IV pili perform motility functions as in bacterial flagella.
A short pilus called Fimbria – latin name for “fringe” is used for attachment to surfaces of host by bacteria and during biofilm production. Pili is also referred to as a virulence factor in pathogenic bacteria strains as it enables such bacteria (e.g E. coli and Vibrio cholerae) to adhere to the receptor on the surface of their host and cause disease.