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A pilus (Latin
Latin

Latin is an Italic language, historically spoken in Latium and Ancient Rome. Through the Military history of the Roman Empire, Latin spread throughout the Mediterranean and a large part of Europe....
 for 'hair'; plural : pili) is a hairlike appendage found on the surface of many bacteria. The terms pilus and fimbria
Fimbria (bacteriology)

In bacteriology, fimbria is a protein appendage in many gram-negative bacteria that is thinner and shorter than a flagellum. This appendage ranges from 3-10 nanometers in diameter and can be up to several micrometers long....
 (Latin for 'thread' or 'fiber'; plural: fimbriae) are often used interchangeably, although some researchers reserve the term pilus for the sexual appendage required for bacterial conjugation
Bacterial conjugation

Bacterial conjugation is the transfer of genetic material between bacteria through direct cell-to-cell contact. Discovered in 1946 by Joshua Lederberg and Edward Tatum, conjugation is a mechanism of horizontal gene transfer—as are Transformation and Transduction —although these mechanisms do not involve cell-to-cell contact....
. All pili are primarily composed of oligomer
Oligomer

In chemistry, an oligomer consists of a limited number of monomer units , in contrast to a polymer which, at least in principle, consists of an unbounded number of monomers....
ic pilin
Pilin

Pilin refers to a class of fibrous proteins that are found in pilus structures in bacteria. Bacterial pili are used in the exchange of genetic material during bacterial conjugation, and a short pilus called a fimbrium is used as a cell adhesion mechanism....
 proteins.

Pili
Pili connect a bacterium to another of its species, or to another bacterium of a different species, and build a bridge between the cytoplasm
Cytoplasm

The cytoplasm is the part of a Cell that is enclosed within the plasma membrane. In eukaryote cells the cytoplasm contains organelles, such as mitochondrion, that are filled with liquid kept separate from the rest of the cytoplasm by biological membranes....
s of the cell
Cell (biology)

The cell is the structural and functional unit of all known Life organisms. It is the smallest unit of an organism that is classified as living, and is often called the building bricks of life....
s.






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A pilus (Latin
Latin

Latin is an Italic language, historically spoken in Latium and Ancient Rome. Through the Military history of the Roman Empire, Latin spread throughout the Mediterranean and a large part of Europe....
 for 'hair'; plural : pili) is a hairlike appendage found on the surface of many bacteria. The terms pilus and fimbria
Fimbria (bacteriology)

In bacteriology, fimbria is a protein appendage in many gram-negative bacteria that is thinner and shorter than a flagellum. This appendage ranges from 3-10 nanometers in diameter and can be up to several micrometers long....
 (Latin for 'thread' or 'fiber'; plural: fimbriae) are often used interchangeably, although some researchers reserve the term pilus for the sexual appendage required for bacterial conjugation
Bacterial conjugation

Bacterial conjugation is the transfer of genetic material between bacteria through direct cell-to-cell contact. Discovered in 1946 by Joshua Lederberg and Edward Tatum, conjugation is a mechanism of horizontal gene transfer—as are Transformation and Transduction —although these mechanisms do not involve cell-to-cell contact....
. All pili are primarily composed of oligomer
Oligomer

In chemistry, an oligomer consists of a limited number of monomer units , in contrast to a polymer which, at least in principle, consists of an unbounded number of monomers....
ic pilin
Pilin

Pilin refers to a class of fibrous proteins that are found in pilus structures in bacteria. Bacterial pili are used in the exchange of genetic material during bacterial conjugation, and a short pilus called a fimbrium is used as a cell adhesion mechanism....
 proteins.

Pili


Pili connect a bacterium to another of its species, or to another bacterium of a different species, and build a bridge between the cytoplasm
Cytoplasm

The cytoplasm is the part of a Cell that is enclosed within the plasma membrane. In eukaryote cells the cytoplasm contains organelles, such as mitochondrion, that are filled with liquid kept separate from the rest of the cytoplasm by biological membranes....
s of the cell
Cell (biology)

The cell is the structural and functional unit of all known Life organisms. It is the smallest unit of an organism that is classified as living, and is often called the building bricks of life....
s. This enables the transfer of plasmid
Plasmid

File:plasmid .svgA plasmid is an extra-chromosomal DNA molecule separate from the chromosome which is capable of replicating independently of the chromosomal DNA....
s between the bacteria. An exchanged plasmid can code for new functions, e.g., antibiotic resistance
Antibiotic resistance

Antibiotic resistance is the ability of a microorganism to withstand the effects of antibiotics. It is a specific type of drug resistance. Antibiotic resistance evolves via natural selection acting upon random mutation, but it can also be engineered by applying an evolutionary stress on a population....
.

Up to ten of these structures can exist on the bacteria. Some bacterial viruses or bacteriophage
Bacteriophage

A bacteriophage is any one of a number of viruses that infection bacteria. The term is commonly used in its shortened form, phage.Typically, bacteriophages consist of an outer protein hull enclosing genetic material....
s attach to receptor
Receptor (biochemistry)

In biochemistry, a receptor is a protein molecule, embedded in either the plasma membrane or cytoplasm of a cell, to which a mobile signaling molecule may attach....
s on sex pili at the start of their reproductive cycle.

Sex pili

Despite its name, the sex pilus is not used for sexual reproduction
Sexual reproduction

Sexual reproduction is characterized by processes that pass a Genetic recombination of Genetics material to offspring, resulting in Genetic diversity....
, and cannot be equated with a penis
Penis

The penis is an external sex organ of certain biologically male organisms, in both vertebrates and invertebrates.The penis is a reproductive organ, technically an intromittent organ, and for Eutheria, additionally serves as the external organ of urination....
, although such comparisons are often used to ease understanding.

A pilus is typically 6 to 7 nm in diameter. During bacterial conjugation
Bacterial conjugation

Bacterial conjugation is the transfer of genetic material between bacteria through direct cell-to-cell contact. Discovered in 1946 by Joshua Lederberg and Edward Tatum, conjugation is a mechanism of horizontal gene transfer—as are Transformation and Transduction —although these mechanisms do not involve cell-to-cell contact....
, a sex pilus emerging from one bacterium ensnares the recipient bacterium, draws it in, and eventually triggers the formation of a mating bridge, which is direct contact merging the cytoplasms of two bacteria via a controlled pore. This pore allows for the transfer of bacterial DNA
DNA

Deoxyribonucleic acid is a nucleic acid that contains the genetics instructions used in the development and functioning of all known living organisms and some viruses....
 from the bacteria with the pilus (donor) to the recipient bacteria. Through this mechanism of genetic
Genetic engineering

Engineering There are a number of ways through which genetic engineering is accomplished. Essentially, the process has five main steps# Isolation of the genes of interest...
 transformation
Transformation (genetics)

In molecular biology, transformation is the Introduction to genetics alteration of a cell resulting from the uptake, genomic incorporation, and expression of foreign genetic material ....
, advantageous genetic traits can be disseminated amongst a population of bacteria. Not all bacteria have the ability to create sex pili, however sex pili can form between bacteria of different species.

The fertility factor is required to produce sex pili.

IV pili

Some pili, designated type IV pili, generate motile
Motility

Motility is a biology term which refers to the ability to move spontaneously and actively, consuming energy in the process. It can apply to either single-celled or multicellular organisms....
 forces. The external termini of the pili adhere to solid substrate, either the surface to which the bacteria are attached or to other bacteria, and subsequent pilus contraction pulls the bacteria forward, not unlike a grappling hook. As type IV pilus-mediated movement is typically jerky, it is called twitching motility, as distinct from other forms of bacterial motility, such as are mediated by flagella. However, in Myxococcus xanthus
Myxococcus xanthus

Myxococcus xanthus exists as a self-organized, Predation , saprotrophic, single-species biofilm called a swarm. Myxococcus xanthus, which can be found almost ubiquitously in soil, consists of thin Bacilli, gram-negative cells that exhibit self-organizing behavior as a response to environmental cues....
, this movement is quite fluid.

Fimbriae


Attachment of bacteria to host surfaces is required for colonization during infection or to initiate formation of a biofilm
Biofilm

A biofilm is a structured community of microorganisms encapsulated within a self-developed polymeric matrix and adherent to a living or inert surface....
. A fimbria
Fimbria (bacteriology)

In bacteriology, fimbria is a protein appendage in many gram-negative bacteria that is thinner and shorter than a flagellum. This appendage ranges from 3-10 nanometers in diameter and can be up to several micrometers long....
 is a short pilus that is used to attach the bacterium to a surface. Fimbriae are either located at the poles of a cell, or are evenly spread over its entire surface. Mutant
Mutant

A mutant is an individual, organism, or new genetic character arising or resulting from an instance of mutation, which is a base-pair sequence change within the DNA of a gene or chromosome of an organism resulting in the creation of a new character or Trait not found in the wild type....
 bacteria that lack fimbriae cannot adhere to their usual target surfaces and, thus, cannot cause disease
Disease

A disease or medical condition is an abnormal condition of an organism that impairs bodily functions, associated with specific symptoms and Medical signs....
s.

Some fimbriae can contain lectins. The lectins are necessary to adhere to target cells because they can recognize oligosaccharide
Oligosaccharide

An oligosaccharide is a saccharide polymer containing a small number of component sugars, also known as simple sugars. The name derived from the Greek oligos, meaning "a few"....
 units on the surface of these target cells. Other fimbriae bind to components of the extracellular matrix
Extracellular matrix

In biology, the extracellular matrix is the extracellular part of animal tissue that usually provides structural support to the animal Cell in addition to performing various other important functions....
.

Fimbriae are found in both Gram-negative
Gram-negative

Gram-negative bacteria are those bacteria that do not retain crystal violet dye in the Gram staining protocol. In a Gram stain test, a counterstain is added after the crystal violet, coloring all Gram-negative bacteria with a red or pink color....
 and Gram-positive
Gram-positive

Gram-positive Bacteria are those that are stained dark blue or violet by Gram staining. This is in contrast to Gram-negative bacteria, which cannot retain the crystal violet stain, instead taking up the counterstain and appearing red or pink....
 bacteria. In Gram positive bacteria, the pilin subunits are covalently linked.

See also


  • Flagellum
    Flagellum

    A flagellum is a tail-like structure that projects from the cell body of certain prokaryotic and eukaryotic cells, and it functions in locomotion....


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