The flagellum or flagella (plural) in bacteria allow the cells to move from one place to another in a liquid medium. This movement can aid in survival for the bacterial cells, allowing them to move to a more nutrient-rich environment if their current location loses nutrient content.
The flagellum consists of a group of proteins oriented into a rotor, hook and tail. The ability of the rotor to turn about a solid base is driven by the proton motive force. The proton motive force refers to the buildup of protons across the cell membrane. Protons in this gradient then move back across the cell membrane, creating the energy used to drive the “motor” of the flagellum, allowing it to rotate.
The names used to identify the different types of flagellations indicate the location of the flagella on the cell. A monotrichous flagellum is located on one end of the bacterial cell. The flagellum, embedded in the double cell membrane of the bacterial cell, rotates around counter-clockwise. This rotation drives the bacterial cell forward.
Amphitrichous flagella are located at each end of the bacterial cell. The increased number of flagella and the arrangement on both ends of the cell allow the bacteria to move from standstill to forward or reverse directly. With a monotrichous flagellum, the bacteria can only move in one direction, and maneuvering is more difficult.
The flagella in a lophotrichous arrangement are situated on one end of the bacterial cell, as with a monotrichous flagellum. However, instead of just one flagellum, multiple flagella help drive the cell forward. With more flagella working at the same time, the bacterial cell can move faster from point A to point B, notes the textbook “Microbiology: 6th edition.”
The peritrichous flagella are located randomly over the surface of the bacterial cell. Many flagella exist in the peritrichous orientation, and can cover the entire cell. These bacteria can easily move in any direction needed. This is especially useful when trying to move toward areas of nutrients, or away from areas that contain no nutrients or other potentially harmful substances.
- University of Illinois at Urbana-Champaign: The Flagellum and Bacterial Motility
- "Microbiology: 6th Edition"; Lansing Prescott, John Harley and Donald Klein; 2005