Pilus
A pilus (
Dozens of these structures can exist on the bacterial and archaeal surface. Some bacteria, viruses or bacteriophages attach to receptors on pili at the start of their reproductive cycle.
Pili are
Types by function
A few names are given to different types of pili by their function. The classification does not always overlap with the structural or evolutionary-based types, as convergent evolution occurs.[3]
Conjugative pili
Conjugative pili allow for the transfer of
A sex pilus is typically 6 to 7
Hyperthermophilic archaea encode pili structurally similar to the bacterial conjugative pili.[6] However, unlike in bacteria, where conjugation apparatus typically mediates the transfer of mobile genetic elements, such as plasmids or transposons, the conjugative machinery of hyperthermophilic archaea, called Ced (Crenarchaeal system for exchange of DNA)[7] and Ted (Thermoproteales system for exchange of DNA),[6] appears to be responsible for the transfer of cellular DNA between members of the same species. It has been suggested that in these archaea the conjugation machinery has been fully domesticated for promoting DNA repair through homologous recombination rather than spread of mobile genetic elements.[6]
Fimbriae
Fimbria (Latin for 'fringe', pl.: fimbriae) is a term used for a short pilus that is used to attach the bacterium to a surface, sometimes also called an "attachment pilus".[8] The term "fimbria" can refer to many different (structural) types of pilus, as many different types of pili have been used for adhesion, a case of convergent evolution.[3] The Gene Ontology system does not treat fimbriae as a distinct type of appendage, using the generic pilus (GO:0009289) type instead.
This appendage ranges from 3–10 nanometers in diameter and can be as much as several micrometers long. Fimbriae are used by bacteria to adhere to one another and to adhere to animal cells and some inanimate objects. A bacterium can have as many as 1,000 fimbriae. Fimbriae are only visible with the use of an electron microscope. They may be straight or flexible.
Fimbriae possess
Some aerobic bacteria form a very thin layer at the surface of a broth culture. This layer, called a pellicle, consists of many aerobic bacteria that adhere to the surface by their fimbriae. Thus, fimbriae allow the aerobic bacteria to remain both on the broth, from which they take nutrients, and near the air.
Fimbriae are required for the formation of biofilm, as they attach bacteria to host surfaces for colonization during infection. Fimbriae are either located at the poles of a cell or are evenly spread over its entire surface.
This term was also used in a lax sense to refer to all pili, by those who use "pilus" to specifically refer to sex pili.[9]
Types by assembling system or structure
chaperone-Usher fimbriae built by T7SS, extracellular nucleation-precipitation pili built by T8SS (including curli), LPXTG including type 3 pilus (T3P; spaHIG)[3]. . (December 2020) |
Transfer
The Tra (transfer) family includes all known sex pili (as of 2010). They are related to the type IV secretion system (T4SS).[3] They can be classified into the F-like type (after the F-pilus) and the P-like type. Like their secretion counterparts, the pilus injects material, DNA in this case, into another cell.[10]
Type IV pili
Some pili, called type IV pili (T4P), generate
This family was originally identified as "type IV fimbriae" by their appearance under the microscope. This classification survived as it happens to correspond to a clade.[18]
Type 1 fimbriae
Another type are called type 1 fimbriae.
Curli
"Gram-negative bacteria assemble functional amyloid surface fibers called curli."[23] Curli are a type of fimbriae.[19] Curli are composed of proteins called curlins.[23] Some of the genes involved are CsgA, CsgB, CsgC, CsgD, CsgE, CsgF, and CsgG.[23]
Virulence
Pili are responsible for virulence in the pathogenic strains of many bacteria, including E. coli, Vibrio cholerae, and many strains of Streptococcus.[24][25] This is because the presence of pili greatly enhances bacteria's ability to bind to body tissues, which then increases replication rates and ability to interact with the host organism.[24] If a species of bacteria has multiple strains but only some are pathogenic, it is likely that the pathogenic strains will have pili while the nonpathogenic strains do not.[26][27]
The development of attachment pili may then result in the development of further virulence traits. Fimbriae are one of the primary mechanisms of virulence for E. coli, Bordetella pertussis, Staphylococcus and Streptococcus bacteria. Their presence greatly enhances the bacteria's ability to attach to the host and cause disease.[28] Nonpathogenic strains of V. cholerae first evolved pili, allowing them to bind to human tissues and form microcolonies.[24][27] These pili then served as binding sites for the lysogenic bacteriophage that carries the disease-causing toxin.[24][27] The gene for this toxin, once incorporated into the bacterium's genome, is expressed when the gene coding for the pilus is expressed (hence the name "toxin mediated pilus").[24]
See also
References
- ^ "pilus" at Dorland's Medical Dictionary
- PMID 13230101.
- ^ PMID 24133488.
- ^ "Gut bacteria use super-polymers to dodge antibiotics | Imperial News | Imperial College London". Imperial News.
- PMID 37019921.
- ^ PMID 36750723.
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- S2CID 860681.
- PMID 1180526.
- PMID 20418394.
- OCLC 951925510.
- PMID 12142488.
- ISBN 978-1-904455-48-6.
- PMID 31110358.
- PMID 23386723.
- PMID 14960717.
- PMID 19464092.
- PMID 18063717.
- ^ PMID 12398210.
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- PMID 16236807.
- ^ WI, Kenneth Todar, Madison. "Colonization and Invasion by Bacterial Pathogens". www.textbookofbacteriology.net. Retrieved 2016-12-03.
{{cite web}}
: CS1 maint: multiple names: authors list (link) - ^ PMID 19011034.
- ^ ISBN 978-1-78064-255-0.
- ISBN 978-1-78064-255-0.
- ^ Todar, Kenneth. "Textbook of Bacteriology: Bacterial Structure in Relationship to Pathogenicity". Textbook of Bacteriology. Retrieved 24 November 2017.
- ^ ISBN 978-1-78064-255-0.
- PMID 8790416.
External links
- Sex+Pilus at the U.S. National Library of Medicine Medical Subject Headings (MeSH)
- Bacterial+Pilus at the U.S. National Library of Medicine Medical Subject Headings (MeSH)
- Fimbriae+Proteins at the U.S. National Library of Medicine Medical Subject Headings (MeSH)