The Beguiling Motility of the Genus Treponema
Nyles W. Charon, Chunhao Li and Stuart F. Goldstein
from: Pathogenic Treponema: Molecular and Cellular Biology (Edited by: Justin D. Radolf and Sheila A. Lukehart). Caister Academic Press, U.K. (2006)
Abstract
Understanding the motility of Treponema species is still at its infancy. An analysis of motility mutants indicate that the periplasmic flagella, which are situated between the outer membrane sheath and cell cylinder, are directly involved in the motility in both Treponema denticola and Treponema phagedenis. Furthermore, not only do these organelles rotate in a manner similar to the flagella of rod-shaped bacteria, but they also have a skeletal function, i.e., they influence the shape of the cell of both species. A model of how these two species swim states the following: During cell displacement, the periplasmic flagella rotate in one direction (counter-clockwise) as viewed from behind the cell, and the right-handed cell cylinder rolls in the opposite direction (clockwise). Because a gel-like medium is essential for translocation of both these spirochetes, this rolling of the cell cylinder is essential for cell displacement. In contrast, almost nothing is known about the dynamics of motility of Treponema pallidum. The organelle for motility, the periplasmic flagellum, has been studied in some detail in these three species. Its structure is unique, as a protein sheath composed of FlaA surrounds a core of three different FlaB proteins, FlaB1, FlaB3, and FlaB3. Although the function of each protein is unclear, recent results with a related spirochete species suggest that some of these proteins have an overlap in function. Specifically, in Brachyspira hyodysenteriae, mutants that lack FlaB1 or FlaB2 are still motile, but mutants that lack both are completely non-motile. Genomic analysis of T. denticola and T. pallidum reveal that both species have all the necessary genes for flagella based motility. Although sequence analysis indicates that their motility genes are well conserved between these species, their gene order is quite different. Furthermore, several lines of evidence indicate that motility gene regulation is controlled at both the transcriptional and translational levels. Finally, because a large number of genes in both species are dedicated to motility, this cell function likely plays an important role in its survival and disease progression in the host. However, there is no experimental evidence as yet to support this contention read more ...
