Bacteria may run towards food sources or away from toxins. When running, flagella rotate counterclockwise so that the bacteria moves forward. 

Running (Bacterial Movement)

Bacteria tumble when they are not moving in a significant forward direction but are repositioning their direction to move. When tumbling, the flagella are moving clockwise and are splayed out.

Tumbling (Bacterial Movement)

There are two types of bacterial movements that are facilitated by flagella: 
- Running
- Tumbling

University of Wisconsin - Madison

Flagella are hair like filaments that extend from the cytoplasmic membrane to the external part of the cell. The flagella functions in cell motility. 

Flagella

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Microbiology covers the scope and sequence requirements for a single-semester microbiology course for non-majors. The book presents the core concepts of microbiology with a focus on applications for careers in allied health. The pedagogical features of the text make the material interesting and accessible while maintaining the career-application focus and scientific rigor inherent in the subject matter. Microbiology’s art program enhances students’ understanding of concepts through clear and effective illustrations, diagrams, and photographs.

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The flagella is composed of the filament, hook and basal body. The hook and filament are composed of protein subunits called flagellin, which is synthesized within the cell. The filament extends outside the cell wall and is connected to the hook at the surface of the cell. The hook and basal body are embedded in the cellular envelope. 

Structure of the Flagella

Directional Movement of Bacteria

There are many environmental signals bacteria sense that influence their movement in the form of a taxis. These taxes are: 
- Phototaxis
- Magnetotaxis
- Chemotaxis

Taxis Influencing Bacterial Movement 

The arrangement of the flagella is organized into four types:
- Monotrichous 
- Lophotrichous
- Amphitrichous 
- Peritrichous 

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