The flagella rotate and move the bacterium in a fashion similar to a propellor. Gram positive bacteria have one set of rings which anchor the flagellum into the cell while gram negative cells have two sets of rings. Flagella may also be identified by special staining techniques. Functions of flagella Primarily function in motility. Positive taxis is movement toward a favorable environment whereas negative taxis is movement away from a repellent.
Flagella can help in identifying certain types of bacteria.
For example, Proteus species show a rapid 'swarming' type of growth on solid media. Flagellar antigens are used to distinguish different species and strains of bacteria known as serovars . H antigen are used in such typing. The filament consists of bundles of small fibrils existing between the cell wall and a multi-layer, flexible outer membrane sheath. When the filaments rotate this causes the cell to turn in a corkscrew-like manner.