During a run, the flagella of a bacterium rotate in a counterclockwise direction, allowing the cell to move forward. In peritrichous bacteria, this counterclockwise rotation causes the flagella to bundle together in a streamlined manner, resulting in efficient, linear movement.

Running (Bacterial Movement)

During a tumble, the flagella of a bacterium rotate in a clockwise direction and splay out, creating a looping motion. This halts forward progress and allows the cell to reorient itself toward the direction of an attractant.

Tumbling (Bacterial Movement)

The directional movement of a bacterium is determined by the configuration of its flagella. Bacteria navigate their environment by alternating between two primary states: running (moving forward via counterclockwise flagellar rotation) and tumbling (reorienting via clockwise flagellar rotation).

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Flagella (singular: flagellum) are tail-like cellular structures used for locomotion by some bacteria, archaea, and eukaryotes. Because they are extremely thin, they typically cannot be observed under a standard light microscope without specialized staining techniques.

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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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 

Arrangement of Flagella

Flagella staining is a specialized technique used to visualize flagella under a light microscope. Because flagella are extremely thin, the procedure first applies a mordant—typically tannic acid or potassium alum—to coat and thicken the flagellum. Following the mordant, the specimen is stained with a dye, most commonly pararosaniline or basic fuchsin, rendering the thickened flagella visible.

Flagella Stain

Bacterial flagella consist of three main parts: a stiff spiral filament composed of flagellin protein subunits, a hook region, and a basal body that acts as a motor embedded in the plasma membrane.

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