M. xanthus is a soil bacterium which commonly grows in damp soil rich in organic matter. The bacteria are rod shaped and 10 times bigger than E. coli in size. They use peptides, lipids and other macromolecules for nutrition and tend to form large multicellular communities, which feed upon other microrganisms, utilizing extracellular antibiotics and degradative enzymes to immobilize and digest their prey (see movie in which Myxo (right) devours a colony of E. coli (left))(4, 5, 10).
(M. xanthus cell and biofilm pictures
M. xanthus is one of many diverse Gram-negative bacteria which move by gliding motility. Gliding motility is traditionally described as movement in the direction of the long axis of the cell at a solid-liquid, solid-air or an air-liquid interface without the aid of flagella (7). M. xanthus has two genetically distinct systems for gliding. The first system is called social (S)-motility and involves the movement of cells in groups (3). The second system is called adventurous (A)-motility and involves the movement of single cells. S-motility requires type IV pili, lipopolysaccharide (LPS) O-antigen, and extracellular matrix polysaccharide (called fibrils). In particular, S-motility has been shown to be powered by type IV pili: pili are extruded from one cell pole and adhere to a surface or to another cell; retraction of the pilus then pulls the cell in the direction of the site of adhesion (1, 2, 6, 11). A- motility is not well understood. The traditional hypothesis assumes the extrusion of a polyelectrolyte gel to push the cell forward (12). A more recent model proposes that intracellular motor complexes, connected to both membrane-spanning adhesion complexes and to the cytoskeleton, power motility by pushing against the substratum and moving the cell body forward, much like focal adhesion-based traction or apicomplexan gliding motility in eukaryotic organisms (8).
M. xanhus cells periodically reverse their direction of gliding (see movie on the right) and cell reversal are thought to be required for directional adjustment as part of the biased random walk necessary for chemotaxis.
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