ABSTRACT
Despite their small size and minimalist construction, most bacteria are nevertheless able to swim. Evidently, the cost of making and operating flagella accords cells a survival advantage over nonmotile species. Although too small to sense a gradient along the length of the cell, and unable to swim long distances because of buffeting by Brownian motion, bacteria can bias their random swimming toward more favorable locations. Bacteria that have lost their flagella by breakage grow new ones, flagellin molecules for this purpose being synthesized in the cell and assembled at the distal tip of the flagellum. Since the bacterial flagellum is a helical structure, rotation in one direction has a different hydrodynamic consequence to rotation in the other. The theoretical possibility has been put forward, that receptors clustered on the bacterial surface could be sufficiently close to interact with each other. An intriguing phenomenon that depends on chemotactic behavior is the formation of large-scale patterns in cultures of bacteria.
