2.1. Bacterial Motility
Many but not all bacteria display motility, i.e. self-propelled motion under appropriate circumstances and this can be achieved by any one of the three mechanisms. Most motile bacteria move by virtue of flagella, rigid structures about 20nm in diameter and 15-20µm long which protrude from the cell surface. Some bacteria have a single flagellum at an end- such cells are called monotrichous. Bacteria having single flagellum at both ends are said to be amphitrichous. Lophotrichous bacteria represent cells having at tuft of flagella at one end whereas peritrichous bacteria possess numerous flagella distributed all over the cell surface (Figure 2.1.). Figure 2.1. Arrangement of Flagella.
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The axial filament present is responsible for rotation of cell in a spiral fashion and thus locomotion (Figure 2.2.). Figure 2.2. Axial filament wrapping around a Spirochete.
The third and final mechanism behind locomotion is gliding motility which is generally the movement of cell over a surface without the aid of flagella. This gliding action is driven by two distinct genetic systems: the adventurous (A-engine) which allow cells to move independently and social (S-engine) motility systems which is activated when cells are in close proximity to each other. The S-engine consists of pili which are flayed outward and provides a pull along while the A-engine operates by secreting slime ribbons providing a push (Figure 2.3.). Figure 2.3. Gliding action is