Struce & Types of Flagella

Structure of Bacterial Flagella

Flagella are helical shaped structure which is composed of subunits of a protein called flagellin. The wider region at the base of the flagellum is called hook. It is different in structure than that of the filament. Hook connects filament to the motor portion of the flagellum called basal body.
The basal body is anchored in the cytoplasmic membrane and cell wall. There are presence of rings which are surrounded by a pair of proteins called Mot. These proteins actually drive the flagellar motor causing rotation of the filament . Another set of proteins called Fli proteins function as the motor switch, reversing rotation of the flagella in response to intra-cellular signals.  (See the image on the right side)
Arrangement and Types of Bacterial Flagella The number and location of flagella are distinctive for each genus. There are four types of flagellar arrangement.

1. Monotrichous (Mono means one): Single polar flagellum e.g. Vibrio cholerae, Campylobacter (polar flagella often in pairs to give a “seagull” appearance).
2. Amphitrichous: Single flagellum at both ends e.g. Alcaligenes faecalis  (Mneomonics: Remember: the characteristics of Amphibians: live both in land and water)
3. Lophotrichous: Tuft of flagella at one or both ends e.g. Spirilla
4. Peritrichous (means flagella in periphery): Flagella surrounding the cell, e.g. Salmonella typhi, Proteus spp (highly motile organism; shows swarming motility)

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