Pilus

Pilus (plural: pili) is a hair-like appendage found on the surface of many bacteria and archaea. The terms pilus and fimbria (plural: fimbriae) can be used interchangeably, although some researchers reserve the term pilus for the appendage required for bacterial conjugation. All pili in the latter sense are primarily composed of pilin proteins.

Structure and Composition

Pili are typically composed of thousands of identical protein subunits known as pilins. The precise composition and arrangement of these pilins can vary between different types of pili and different bacterial species. The pilin protein molecules are assembled into a helical chain, with a hollow core running the length of the pilus.

Functions

Pili have several functions for bacteria, including:

• Adhesion: Pili allow bacteria to attach to other cells or surfaces. This is often the first step in colonization and infection of a host organism.
• Conjugation: Some types of pili, known as sex pili, allow for the transfer of DNA between bacterial cells in a process known as bacterial conjugation.
• Movement: Some bacteria can use their pili to move across surfaces in a process known as twitching motility.

Types of Pili

There are several types of pili, including:

• Type IV Pili: These are involved in twitching motility and DNA uptake.
• Type I Pili: These are involved in adhesion to surfaces and other cells.
• Sex Pili: These are involved in bacterial conjugation.

See Also

• Bacteria
• Bacterial conjugation
• Fimbria (bacteriology)

References

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  Conjugation
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  Bacterial conjugation
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  Beltran et al Fig5
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  E. coli fimbriae
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  Type IV Pilus Twitching Motility Steps
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  Type IVa pilus machine architectural model
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  Fimbriae Adhesion to a Host Cell