Joined: May 2002
Some interesting tidbits on the adhesion-related function of flagella:
Flagella, which act as semirigid helical propellers, provide bacteria with a highly efficient means of locomotion. For example, many Vibrio and Pseudomonas species swim in liquid environments at speeds as fast as 60 µm/s (10, 11, 64, 189). The propellers are powered by reversible rotary motors embedded in the cell membrane, which can turn the flagellum at rates as high as 1,700 revolutions per s (rps) (115). Energy for rotation of the motor is derived from either the sodium or proton membrane potential (72, 117). The number and arrangement of the propellers can vary, but the mode of insertion is of two major types, i.e., polar or peritrichous. Flagella play other roles in addition to swimming in liquid (reviewed in reference 132). They can enable bacteria to move over and colonize surfaces, a process called swarming (63). They also participate in adhesion. Attachment of bacteria to surfaces is often first mediated by contact of the flagellum with the surface (127). As propulsive organelles, flagella seems to aid in overcoming negative electrostatic interactions and thus are believed to play a key role in the initial steps of adsorption of bacteria to surfaces, biofilm formation, and invasion of hosts (30, 39, 154). Studies using Vibrio alginolyticus have demonstrated that attachment to glass is directly proportional to swimming speed (90). Other studies have shown that by disabling the flagellar motor of the fish pathogen V. anguillarum, invasion into the fish host is severely reduced (142). In addition, some flagella are sheathed by a membrane that appears to be an extension of the outer cell membrane. The composition of this sheath (specifically, lipopolysaccharide and protein) may allow additional specific interactions between the bacterium and a surface (77, 163, 164).
Some of the refs:
Crit Rev Microbiol 1996;22(2):67-100
Functions of bacterial flagella.
Moens S, Vanderleyden J.
F. A. Janssens Laboratory of Genetics, Katholieke Universiteit Leuven, Heverlee, Belgium.
Many bacterial species are motile by means of flagella. The structure and implantation of flagella seems related to the specific environments the cells live in. In some cases, the bacteria even adapt their flagellation pattern in response to the environmental conditions they encounter. Swarming cell differentiation is a remarkable example of this phenomenon. Flagella seem to have more functions than providing motility alone. For many pathogenic species, studies have been performed on the contribution of flagella to the virulence, but the result is not clear in all cases. Flagella are generally accepted as being important virulence factors, and expression and repression of flagellation and virulence have in several cases been shown to be linked. Providing motility is always an important feature of flagella of pathogenic bacteria, but adhesive and other properties also have been attributed to these flagella. In nonpathogenic bacterial colonization, flagella are important locomotive and adhesive organelles as well. In several cases where competition between several bacterial species exists, motility by means of flagella is shown to provide a specific advantage for a bacterium. This review gives an overview of studies that have been performed on the significance of flagellation in a wide variety of processes where flagellated bacteria are involved.
133. Motaleb, M. A., L. Corum, J. L. Bono, A. F. Elias, P. Rosa, D. S. Samuels, and N. W. Charon. 2000. Borrelia burgdorferi periplasmic flagella have both skeletal and motility functions. Proc. Natl. Acad. Sci. USA 97:10899-10904 Abstract/Free Full Text.
And, regarding the poor man's alternative to flagella, gas vesicles:
Department of Botany, University of Bristol, England.
The gas vesicle is a hollow structure made of protein. It usually has the form of a cylindrical tube closed by conical end caps. Gas vesicles occur in five phyla of the Bacteria and two groups of the Archaea, but they are mostly restricted to planktonic microorganisms, in which they provide buoyancy. By regulating their relative gas vesicle content aquatic microbes are able to perform vertical migrations. In slowly growing organisms such movements are made more efficiently than by swimming with flagella. The gas vesicle is impermeable to liquid water, but it is highly permeable to gases and is normally filled with air. It is a rigid structure of low compressibility, but it collapses flat under a certain critical pressure and buoyancy is then lost. Gas vesicles in different organisms vary in width, from 45 to > 200 nm; in accordance with engineering principles the narrower ones are stronger (have higher critical pressures) than wide ones, but they contain less gas space per wall volume and are therefore less efficient at providing buoyancy. A survey of gas-vacuolate cyanobacteria reveals that there has been natural selection for gas vesicles of the maximum width permitted by the pressure encountered in the natural environment, which is mainly determined by cell turgor pressure and water depth. Gas vesicle width is genetically determined, perhaps through the amino acid sequence of one of the constituent proteins. Up to 14 genes have been implicated in gas vesicle production, but so far the products of only two have been shown to be present in the gas vesicle: GvpA makes the ribs that form the structure, and GvpC binds to the outside of the ribs and stiffens the structure against collapse. The evolution of the gas vesicle is discussed in relation to the homologies of these proteins.