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Gliding motility is a type of translocation used by
microorganism A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in old ...
s that is independent of propulsive structures such as
flagella A flagellum (; ) is a hairlike appendage that protrudes from certain plant and animal sperm cells, and from a wide range of microorganisms to provide motility. Many protists with flagella are termed as flagellates. A microorganism may have fro ...
,
pili Pili may refer to: Common names of plants * '' Canarium ovatum'', a Philippine tree that is a source of the pili nut * ''Heteropogon contortus'', a Hawaiian grass used to thatch structures Places * Pili, Camarines Sur, is a municipality in the ...
, and fimbriae. Gliding allows microorganisms to travel along the surface of low aqueous films. The mechanisms of this motility are only partially known. Twitching motility also allows microorganisms to travel along a surface, but this type of movement is jerky and uses
pili Pili may refer to: Common names of plants * '' Canarium ovatum'', a Philippine tree that is a source of the pili nut * ''Heteropogon contortus'', a Hawaiian grass used to thatch structures Places * Pili, Camarines Sur, is a municipality in the ...
as its means of transport. Bacterial gliding is a type of gliding motility that can also use pili for propulsion. The speed of gliding varies between organisms, and the reversal of direction is seemingly regulated by some sort of internal clock. For example the
apicomplexan The Apicomplexa (also called Apicomplexia) are a large phylum of parasitic alveolates. Most of them possess a unique form of organelle that comprises a type of non-photosynthetic plastid called an apicoplast, and an apical complex structure. The ...
s are able to travel at fast rates between 1–10 µm/s. In contrast '' Myxococcus xanthus'' bacteria glide at a rate of 0.08 µm/s. Cell-invasion and gliding motility have TRAP ( thrombospondin-related anonymous protein), a surface protein, as a common molecular basis that is both essential for infection and locomotion of the invasive apicomplexan parasite. Micronemes are secretory organelles on the apical surface of the apicomplexans used for gliding motility. In the diagram above, right:


Types of motility

Bacterial gliding is a process of motility whereby a
bacterium Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were am ...
can move under its own power. Generally, the process occurs whereby the bacterium moves along a surface in the general direction of its long axis. Gliding may occur via distinctly different mechanisms, depending on the type of bacterium. This type of movement has been observed in phylogenetically diverse bacteria such as
cyanobacteria Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, bl ...
, myxobacteria,
cytophaga ''Cytophaga'' is a genus of Gram-negative, gliding, rod-shaped bacteria. This bacterium is commonly found in soil, rapidly digests crystalline cellulose ''C. hutchinsonii'' is able to use its gliding motility to move quickly over surfaces. ...
, flavobacteria, and
mycoplasma ''Mycoplasma'' is a genus of bacteria that, like the other members of the class '' Mollicutes'', lack a cell wall around their cell membranes. Peptidoglycan ( murein) is absent. This characteristic makes them naturally resistant to antibioti ...
. Bacteria move in response to varying climates, water content, presence of other organisms, and firmness of surfaces or media. Gliding has been observed in a wide variety of phyla, and though the mechanisms may vary between bacteria, it is currently understood that it takes place in environments with common characteristics, such as firmness and low-water, which enables the bacterium to still have motility in its surroundings. Such environments with low-water content include
biofilm A biofilm comprises any syntrophic consortium of microorganisms in which cells stick to each other and often also to a surface. These adherent cells become embedded within a slimy extracellular matrix that is composed of extracellular po ...
s,
soil Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former ...
or soil crumbs in tilth, and microbial mats.


Purpose

Gliding, as a form of motility, appears to allow for interactions between bacteria,
pathogenesis Pathogenesis is the process by which a disease or disorder develops. It can include factors which contribute not only to the onset of the disease or disorder, but also to its progression and maintenance. The word comes from Greek πάθος ''pat ...
, and increased social behaviours. It may play an important role in
biofilm A biofilm comprises any syntrophic consortium of microorganisms in which cells stick to each other and often also to a surface. These adherent cells become embedded within a slimy extracellular matrix that is composed of extracellular po ...
formation, bacterial
virulence Virulence is a pathogen's or microorganism's ability to cause damage to a host. In most, especially in animal systems, virulence refers to the degree of damage caused by a microbe to its host. The pathogenicity of an organism—its ability to ...
, and chemosensing.


Swarming motility

Swarming motility Swarming motility is a rapid (2–10 μm/s) and coordinated translocation of a bacterial population across solid or semi-solid surfaces, and is an example of bacterial multicellularity and swarm behaviour. Swarming motility was first reported b ...
occurs on softer semi-solid and solid surfaces (which usually involves movement of a bacterial population in a coordinated fashion via
quorum sensing In biology, quorum sensing or quorum signalling (QS) is the ability to detect and respond to cell population density by gene regulation. As one example, QS enables bacteria to restrict the expression of specific genes to the high cell densities at ...
, using flagella to propel them), or twitching motility on solid surfaces (which involves extension and retraction of type IV pili to drag the bacterium forward).


Proposed mechanisms

The mechanism of gliding might differ between species. Examples of such mechanisms include: *
Motor proteins Motor proteins are a class of molecular motors that can move along the cytoplasm of cells. They convert chemical energy into mechanical work by the hydrolysis of ATP. Flagellar rotation, however, is powered by a proton pump. Cellular function ...
found within the inner membrane of the bacteria utilize a proton-conducting channel to transduce a mechanical force to the cell surface. The movement of the
cytoskeletal The cytoskeleton is a complex, dynamic network of interlinking protein filaments present in the cytoplasm of all cells, including those of bacteria and archaea. In eukaryotes, it extends from the cell nucleus to the cell membrane and is compo ...
microfilaments Microfilaments, also called actin filaments, are protein filaments in the cytoplasm of eukaryotic cells that form part of the cytoskeleton. They are primarily composed of polymers of actin, but are modified by and interact with numerous other pr ...
causes a mechanical force which travels to the adhesion complexes on the substrate to move the cell forward. Motor and regulatory proteins that convert intracellular motion into mechanical forces like traction force have been discovered to be a conserved class of intracellular motors in bacteria that have been adapted to produce cell motility. * A-motility ( adventurous motility) as a proposed type of gliding motility, involving transient adhesion complexes fixed to the substrate while the organism moves forward. For example, in '' Myxococcus xanthus'', a social bacterium. * Ejection or secretion of a
polysaccharide Polysaccharides (), or polycarbohydrates, are the most abundant carbohydrates found in food. They are long chain polymeric carbohydrates composed of monosaccharide units bound together by glycosidic linkages. This carbohydrate can react with w ...
slime from nozzles at either end of the cell body. * Energized nano-machinery or large macromolecular assemblies located on the bacterium's cell body. * " Focal adhesion complexes" and "treadmilling" of surface adhesins distributed along the cell body. * The gliding motility of '' Flavobacterium johnsoniae'' uses a helical track superficially similar to ''M. xanthus'', but via a different mechanism. Here the adhesin SprB is propelled along the cell surface (spiraling from pole to pole), pulling the bacterium along 25 times faster than ''M. xanthus''. '' Flavobacterium johnsoniae'' move via a screw-like mechanism and are powered by a proton motive force.


See also

*
Extracellular polymeric substance Extracellular polymeric substances (EPSs) are natural polymers of high molecular weight secreted by microorganisms into their environment. EPSs establish the functional and structural integrity of biofilms, and are considered the fundamental comp ...
* Microneme *
Mucilage Mucilage is a thick, gluey substance produced by nearly all plants and some microorganisms. These microorganisms include protists which use it for their locomotion. The direction of their movement is always opposite to that of the secretion of m ...


References

{{reflist, 22em Cell movement