From Wikipedia,
the free encyclopedia.
Image of bacteriological
pili or fimbriae
A pilus (Latin;
plural : pili) is a
hairlike structure on the surface
of a
cell, especially
Gram-negative
bacteria, a
protein appendage required for
bacterial
conjugation. Pili connect the
bacterium to another of its
species and build a bridge between
the cytoplasm of either cell. That
enables the transfer of
plasmids between the bacteria.
An exchanged plasmid can add new
functions to a bacterium, e.g., an
antibiotic resistance.
Sometimes called a sex pilus
(plural: sex pili). Up to ten of
these structures can exist on the
bacteria. Some bacterial
viruses or bacteriphages
attach to
receptors on sex pili at the
start of their
reproductive cycle.
Despite the name "sex pilus",
this has nothing to do with
sexual reproduction or
mating, nor is it the
bacterial equivalent of a
penis; such
misnomers are used quite
frequently in describing the
process, and while may prove
useful in understanding underlying
concepts are misleading
nonetheless.
A pilus is typically 9 to 10
nm in diameter. The sex pilus
allows for the transfer of
bacterial
DNA from the bacteria with the
pilus (donor) to the recipient
bacteria. Through this mechanism
of
genetic
transformation, 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.
It is an extension of the
cytoplasm and used for
attachment to surfaces (and is
then called a fimbrium) and
conjugation with another cell
of the same
species.
A fimbrium (Latin;
plural: fimbria) (main
article:
fimbria) is a short pilus that
is used to attach the cell to a
surface. Fimbria are either
located at the poles of a cell, or
are evenly spread over its entire
surface.
Mutant bacteria that lack
fimbria cannot adhere to their
usual target surfaces and, thus,
cannot cause
diseases.
Pili generate motile force via
interactions with the bacteria
cytoskeleton MreB which is
homologous to eukaryotic actin.
The process is akin to the myosin
power stroke. The external termini
of the pili adhere to solid
substrate, and subsequent pili
contraction pulls the bacteria
forward, not unlike a grappling
hook.
See also
