Gliding motility is a type of translocation used by

microorganism A microorganism, or microbe, is an organism of microscopic scale, microscopic size, which may exist in its unicellular organism, single-celled form or as a Colony (biology)#Microbial colonies, colony of cells. The possible existence of unseen ...

s that is independent of propulsive structures such as

flagella A flagellum (; : flagella) (Latin for 'whip' or 'scourge') is a hair-like appendage that protrudes from certain plant and animal sperm cells, from fungal spores ( zoospores), and from a wide range of microorganisms to provide motility. Many pr ...

, pili, 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 Twitch may refer to: Biology * Muscle contraction ** Convulsion, rapid and repeated muscle contraction and relaxation ** Fasciculation, a small, local, involuntary muscle contraction ** Myoclonic twitch, a jerk usually caused by sudden muscle co ...

also allows microorganisms to travel along a surface, but this type of movement is jerky and uses pili 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; single: apicomplexan) are organisms of a large phylum of mainly parasitic alveolates. Most possess a unique form of organelle structure that comprises a type of non-photosynthetic plastid called an apico ...

s are able to travel at fast rates between 1–10 μm/s. In contrast ''

Myxococcus xanthus ''Myxococcus xanthus'' is a gram-negative, bacillus (or rod-shaped) species of myxobacteria that is typically found in the top-most layer of soil. These bacteria lack flagella; rather, they use pili for motility. ''M. xanthus'' is well-known fo ...

'' bacteria glide at a rate of 0.08 μm/s.

Types of motility

Bacterial gliding is a process of motility whereby a

bacterium Bacteria (; : 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 among the ...

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 ( ) are a group of autotrophic gram-negative bacteria that can obtain biological energy via oxygenic photosynthesis. The name "cyanobacteria" () refers to their bluish green (cyan) color, which forms the basis of cyanobacteri ...

myxobacteria The myxobacteria ("slime bacteria") are a group of bacteria that predominantly live in the soil and feed on insoluble organic substances. The myxobacteria have very large genomes relative to other bacteria, e.g. 9–10 million nucleotides except ...

cytophaga ''Cytophaga'' is a genus of Gram-negative, gliding, rod-shaped bacteria. This bacterium is commonly found in soil, rapidly digests crystalline cellulose.Home - Cytophaga hutchinsonii ATCC 33406. (n.d.). Retrieved May 02, 2017, from http://genom ...

flavobacteria The class Flavobacteriia is composed of a single class of environmental bacteria. It contains the family Flavobacteriaceae, which is the largest family in the phylum Bacteroidota. This class is widely distributed in soil, fresh, and seawater habi ...

, and

mycoplasma ''Mycoplasma'' is a genus of bacteria that, like the other members of the class ''Mollicutes'', lack a cell wall, and its peptidoglycan, around their cell membrane. The absence of peptidoglycan makes them naturally resistant to antibiotics ...

. 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 is a Syntrophy, syntrophic Microbial consortium, community of microorganisms in which cell (biology), cells cell adhesion, stick to each other and often also to a surface. These adherent cells become embedded within a slimy ext ...

soil Soil, also commonly referred to as earth, is a mixture of organic matter, minerals, gases, water, and organisms that together support the life of plants and soil organisms. Some scientific definitions distinguish dirt from ''soil'' by re ...

or soil crumbs in

tilth Tilth is a physical condition of soil, especially in relation to its suitability for planting or growing a crop. Factors that determine tilth include the formation and stability of aggregated soil particles, moisture content, degree of aeration, ...

, and

microbial mat A microbial mat is a multi-layered sheet or biofilm of microbial colonies, composed of mainly bacteria and/or archaea. Microbial mats grow at interfaces between different types of material, mostly on submerged or moist surfaces, but a few surviv ...

Three types

Three types of gliding motility in bacteria are: a)

Type IV pili A pilus (Latin for 'hair'; : pili) is a hair-like cell-surface appendage found on many bacteria and archaea. The terms ''pilus'' and '' fimbria'' (Latin for 'fringe'; plural: ''fimbriae'') can be used interchangeably, although some researchers ...

: A cell attaches its pili to a surface or object in the direction it is traveling. The proteins in the pili are then broken down to shrink the pili pulling the cell closer to the surface or object that was it was attached to. b) Specific motility membrane proteins: Transmembrane proteins are attached to the host surface. This adhesion complex can either be specific to a certain type of surface like a certain cell type or generic for any solid surface. Motor proteins attached to an inner membrane force the movement of the internal cell structures in relation to the transmembrane proteins creating net movement. This is driven by the proton motive force. The proteins involved differ between species. An example of a bacterium that uses this mechanism would be ''Flavobacterium''. This mechanism is still being studied and is not well understood. c) Polysaccharide jet: The cell releases a 'jet' of polysaccharide material behind it propelling it forward. This polysaccharide material is left behind. Cell-invasion and gliding motility have TRAP (

thrombospondin Thrombospondins (TSPs) are a family of secreted glycoproteins with antiangiogenic functions. Due to their dynamic role within the extracellular matrix they are considered matricellular proteins. The first member of the family, thrombospondin 1 ...

-related anonymous protein), a surface protein, as a common molecular basis that is both essential for infection and locomotion of the invasive apicomplexan parasite.

Microneme Micronemes are secretory organelles, possessed by parasitic apicomplexans. Micronemes are located on the apical third of the protozoan body. They are surrounded by a typical unit membrane. On electron microscopy they have an electron-dense ma ...

s are secretory organelles on the apical surface of the apicomplexans used for gliding motility.

Purpose

Gliding, as a form of motility, appears to allow for interactions between bacteria,

pathogenesis In pathology, 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 . Descript ...

, and increased social behaviours. It may play an important role in

formation, bacterial

virulence Virulence is a pathogen's or microorganism's ability to cause damage to a host. In most cases, especially in animal systems, virulence refers to the degree of damage caused by a microbe to its host. The pathogenicity of an organism—its abili ...

, 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 by ...

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 signaling (QS) is the process of cell-to-cell communication that allows bacteria to detect and respond to cell population density by gene regulation, typically as a means of acclimating to environmental disadv ...

, using flagella to propel them), or

twitching motility Twitch may refer to: Biology * Muscle contraction ** Convulsion, rapid and repeated muscle contraction and relaxation ** Fasciculation, a small, local, involuntary muscle contraction ** Myoclonic twitch, a jerk usually caused by sudden muscle co ...

on solid surfaces (which involves extension and retraction of

type IV pili A pilus (Latin for 'hair'; : pili) is a hair-like cell-surface appendage found on many bacteria and archaea. The terms ''pilus'' and '' fimbria'' (Latin for 'fringe'; plural: ''fimbriae'') can be used interchangeably, although some researchers ...

to drag the bacterium forward).

Proposed mechanisms

The mechanism of gliding might differ between species. Examples of such mechanisms include: *

Motor protein Motor proteins are a class of molecular motors that can move along the cytoskeleton of cells. They do this by converting chemical energy into mechanical work by the hydrolysis of ATP. Cellular functions Motor proteins are the driving force b ...

s 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 Cell (biology), cells, including those of bacteria and archaea. In eukaryotes, it extends from the cell nucleus to the cell membrane ...

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 p ...

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 Adventurous motility is as a type of gliding motility; unlike most motility mechanisms, adventurous motility does not involve a flagellum. Gliding motility usually involves swarms of bacteria; however, adventurous motility is practiced by individ ...

) as a proposed type of gliding motility, involving transient adhesion complexes fixed to the substrate while the organism moves forward. For example, in ''

'', 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 wat ...

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 In cell biology, focal adhesions (also cell–matrix adhesions or FAs) are large macromolecular assemblies through which mechanical force and regulatory signals are transmitted between the extracellular matrix (ECM) and an interacting Cell (biolo ...

complexes" and "treadmilling" of surface adhesins distributed along the cell body. * The gliding motility of ''

Flavobacterium johnsoniae ''Flavobacterium'' is a genus of Gram-negative, nonmotile and motile, rod-shaped bacteria that consists of 130 recognized species. Flavobacteria are found in soil and fresh water in a variety of environments. Several species are known to cause ...

'' 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''. ''

'' move via a screw-like mechanism and are powered by a proton motive force.

References