Lecture 10: Prokaryotic Cell Movements

Why do microbes move?

To respond to stimuli (taxis), such as food, oxygen, light, or harmful substances

What is taxis?

Directed movement in response to a stimulus

What is chemotaxis?

Movement toward or away from chemical stimuli.

What is aerotaxis?

Movement in response to oxygen concentration

What is phototaxis?

Movement in response to light

What is the primary structure bacteria use for movement?

Flagella

What are the different flagella arrangements?

• Peritrichous

• Monotrichous

• Lophotrichous

• Amphitrichous

What are "runs" and "tumbles"?

• Run: Continuous movement in one direction.

• Tumble: Abrupt, random change in direction due to flagellar reversal.

What determines whether a bacterium runs or tumbles?

• Counterclockwise (CCW) rotation = Run

• Clockwise (CW) rotation = Tumble

How do bacteria with polar flagella move?

Some can reverse direction by switching flagellar rotation; others stop and reorient

What are the three main parts of a flagellum?

• Filament: long outer region

• Hook: connects filament to basal body

• Basal body: anchors flagellum

What is the function of the basal body?

Anchors the flagellum to the cell wall and membrane

What are the rings in the basal body?

• L ring (Outer membrane)

• P ring (Peptidoglycan)

• MS and C rings (Cytoplasmic membrane

What proteins power flagellar rotation?

• Mot proteins: motor function

• Fli proteins: motor switch

How does the proton turbine model work?

Protons move through Mot proteins, generating force that rotates the flagellum

How fast can bacterial flagella rotate?

Up to 20,000 rpm with near 100% energy efficiency

What are fimbriae?

Short, hair-like appendages that help bacteria adhere to surfaces

How do fimbriae aid in infection?

Help bacteria attach to host tissues, aiding in colonization and biofilm formation

What are pili?

• Longer than fimbriae, usually 1-2 per cell

• involved in DNA transfer and motility

What is twitching motility?

Type IV pili extend, attach to a surface, then retract, pulling the cell forward

What is gliding motility?

Smooth movement along surfaces, often seen in myxobacteria

What structure allows some bacteria to regulate buoyancy?

Gas vesicles, which help adjust position in the water column.

How do bacteria detect stimuli?

Via transmembrane receptors, which relay signals to flagellar motors

What happens when bacteria encounter an attractant?

More runs and fewer tumbles, leading to movement toward the attractant

What happens when bacteria encounter a repellent?

More tumbles, changing direction to move away

What is an example of aerotaxis?

Aerobic bacteria move toward oxygen, while anaerobes disperse away

What is an example of chemotaxis?

Bacteria cluster around a glucose source (attractant) and move away from carbolic acid (repellent)

What bacteria use twitching motility?

Bacteria with Type IV pili

How do bacteria move in low-water environments?

Gliding motility allows movement across solid surfaces