Bacteria may be motile by a variety of mechanisms, but the most common involves flagella. Procedures that reveal the presence of flagella will thus indicate bacterial motility. Bacteria may possess a single polar flagellum (monotrichous), tufts of flagella at each pole (lophotrichous), one or more flagella at both poles (amphitrichous) or flagella surrounding the perimeter of the cell (peritrichous). Powered by a proton motive force, or in some instances a sodium gradient, the flagellum can rotate up to an astounding 100,000 rpm in the case of some Vibrio sp. thus allowing, in this case, V. alginolyticus bacteria to swim at a maximal rate of 147 mm/sec. Motile bacteria can respond to chemical and light gradients via chemotaxis and phototaxis, respectively. The presence or absence of flagella is important to bacterial survival and growth, and visualization of these appendages by staining and subsequent light microscopy is an important tool for their characterization.
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