The HaloEd Project

A web site dedicated to biotechnology education

Motility

Halobacteria are extremely motile microbes:

· They possess two forms of motility: Flagellar motility and motility imparted by the presence of Gas Vesicles.

· They swim along straight lines by rotating their flagella. They can swim both forwards and backwards, reorienting themselves periodically by tumbling.

· The cells move towards certain desirable chemicals, a process called chemotaxis.

· The cells have color-sensing phototaxis response (swimming toward beneficial green light and away from damaging blue and ultraviolet light).

· They also contain gas vesicles; these are small, intracellular structures, made purely of protein (unlike standard membranes, which contain lipids as well). They are filled with air and enable the cells to float to the surface of bodies of water and increase the availability of light and oxygen to cells.

· When gas vesicles are present, they cause the cells to appear pink and opaque on plates (see Fig. 1 below) and float in liquid cultures (Vac⁺ cells in test-tube, Fig. 2). When absent, colonies appear red and translucent and in liquid cultures, the cells sink to the bottom (Vac^-Fig. 2).