ABSTRACT
Motility confers on the microorganisms the ability to survive in their natural habitats. In order to cope up with environmental conditions of excess or defi ciency of light/nutrients (or chemicals) the microorganisms exhibit necessary adjusting movements. The fi rst organ of motility that attracted the attention of bacterial motility is fl agella. Ever since the discovery of bacteria it has served as an important taxonomic trait to distinguish bacterial species. Motility due to fl agella is present in both eubacteria and archaebacteria. The bacterial fl agella are composed of three parts, a basal body, the hook and the fi lament. The basal body acts as the motor, the hook joins the fi lament to the basal body and the fi lament acts as the propeller. The fi lament is composed of many thousands of molecules of a single protein known as fl agellin and assumes a diameter of 20 nm. There are certain subtle differences between the organization of the proteins of the motor of eubacteria and archaebacteria. Moreover, the polar and lateral fl agella differ in their structure while the former is sheathed and thicker the latter is unsheathed and thinner. In spirochetes the fl agella are unusually located internally in the periplasmic space. Type IV pili (Tfp), junctional pore complex (JPC), ratchet structure and contractile cytoskeleton are the other motility structures present in eubacteria (Bardy et al., 2003). The movements associated with Tfp are known as twitching movements. Pseudomonas aeruginosa and Neisseria gonorrhoeae are the classical examples that exhibit twitching movements. The myxobacterium Myxococcus xanthus exhibits two types of gliding motion, i.e. social gliding
and adventurous gliding. Social gliding is exhibited by groups of cells and adventurous gliding by single cells. It is interesting to note that social gliding is mediated by Tfp. Besides helically arranged protein fi brils, JPC is another organelle that helps M. xanthus in its adventurous gliding (Mattick, 2002; Nudleman and Kaiser, 2004).
