Abstract This report explains in detail the function, structure and assembly of flagella in E.coli and Salmonella, using plain language and a number of diagrams. Movement (chemotaxis) is the primary function of flagella but its design also incorporates efficient repair capability and antigenic variation. In Salmonella and E.coli the flagellar filament is a homopolymer of flagellin monomers, although other species (such as Helicobacter) build their flagella from mixtures of two types of subunit. All the properties of the functioning filament are reflected in the structure of the flagellin monomer, which has conserved and variable regions, regions targeted by chaperones and coiling enzymes and regions evolved specifically for interaction between monomers. Chemotaxis is driven by a proton motive force (as in oxidative phosphorylation) and the basal complex that converts this energy into rapid rotation of the flagellum is highly complex.
From the Paper "Many bacteria are motile and exhibit chemotaxis ? migration through the extracellular medium towards attractants (e.g. carbon sources), and away from repellents (e.g. antibiotics). The majority move using flagella ?protein structures variable in number and position (Box 1) that generate thrust by rotating like propellers. Flagella are 15nm in diameter and can be observed under light microscopy after thick metal staining or using advanced microscopy techniques such as electron microscopy. Because of the competitive advantages of chemotaxis, there has been strong selection for efficient chemotactic apparatus and flagellar efficiency. The flagellum is based in the bacterial surface layers where a complex array of proteins forms the flagellar motor. Resembling the electric rotary motor and the membrane-bound F1F0-ATPase, and powered by a proton influx across the inner membrane, this highly efficient machine is merely 30nm in diameter. Its mechanism is the subject of ongoing research."
