Bacteria that are capable of propelling themselves forward as well as changing direction are called motile bacteria. This ability allows bacteria to flee from predators, move toward nutrients, and react to changes in their environment. Bacterial motility is important for both root colonization and chemotactic behavior and survival. When describing bacteria movement, scientists often also use the words motility and locomotion.
One way that motile bacteria move is by using structures called flagella, which are attached to the bacteria. This is called flagellar movement. Flagella are rigid structures that protrude from the bacteria’s surface. Flagella move like motors in clockwise and counterclockwise directions, propelling the bacteria.
Helical bacteria, also known as the spirochaetes, have internal filaments that allow them to move. These filaments rotate the cell in a spiral fashion, propelling it through the environment. This type of cell movement is called spirochaetal movement.
The third kind of motility that bacteria are capable of is called gliding motility. The exact method of movement by gliding bacteria is unknown, as they do not contain flagella-type structures on their interior or exterior. However, it is known that they secrete a slime to enable this process, similar to the way a snail leaves a trail of slime behind as it travels.
Identifying Motile Bacteria
Bacterial motility can be detected with a microscope. When examining for movement, there is a risk of detecting false movement. False movement is usually the result of air currents or liquid medium particles. Bacteria that are actually moving show a propelling action in a definite direction. This contrasts to bacteria that are nonmotive and may move in a zigzag or directionless formation.
Types of Motile Bacteria
Some bacteria that use flagellar movement include vibrio, spirillum, klebsiella, pseudomonas, azospirillum and salmonella. Bacteria that utilize spirochaetal movement include the borrelia, treponema, leptospira, cristispira and spirochaeta. A few examples of the gliding bacteria include achroonema, alysiella and cyanobacterium Oscillatoria.