Gliding Motility, Protonmotive Force Motor, and Flagellar Rotation

Abstract

Various bacteria move by gliding motility. The prokaryotes that do this come from a wide variety of morphological and taxonomic classes. Four characteristics seem to unify the process (see Burchard, 1981; Pate, 1988); (i) the organisms are all Gram-negative; (ii) gliding motility requires a suitable surface; (iii) slime may be an esssential component of that surface; and (iv) the process is powered by chemiosmosis. There appear to be no other common elements. When these Gram-negative bacteria are viewed microscopically, the means of motion are not evident since flagella are undetectable and their presumed sinusoidal movements are not detected. These observations have increased, rather than decreased, the number of proposed mechanisms. Earlier models, reviewed by Burchard (1981), have invoked forces such as osmotic pressure, surface tension, slime secretion, and contractile cell-surface waves. Other models involve the retraction of fimbriae (MacRae and McCurdy, 1976), make-and-break of envelope interactions with the substrate (Dickson et al., 1986), and “electrokinetic” phenomena. Dworkin and associates (Dworkin et al.,1983; Keller et al., 1983) introduced a model of surfactant release, Pate and Chang (1979) have suggested rotary motors, and Lapidus and Berg (1982) have imagined that gliding cells have continuous tracks under the outer membrane that revolve around the cell. A variant has been proposed by Ridgway and Lewin (1988) in which the limited motion of many mechanically independent domains is functionally coordinated.