2.3 Motility in Bacteria
🚶♂️ Introduction to Bacterial Movement
Not all bacteria stay still! Many can move to find food, escape danger, or explore their environment. Their movement is called motility.
Bacteria can move in different ways, depending on their structure. Let’s look at these types:
🔄 1. Flagellar Movement
- Most rod-shaped (bacilli) and spiral-shaped (spirilla) bacteria use flagella to move.
- A flagellum is like a tiny, whip-like tail that spins like a motor.
- The bacteria swim forward when the flagellum spins counterclockwise.
- If many bacteria move together using their flagella, it’s called swarming.
👣 2. Twitching or Crawling
- This movement happens on solid surfaces, not in water.
- Bacteria use pili—small, hair-like structures—to stick to the surface.
- Then they pull themselves forward, like crawling or twitching.
🧼 3. Gliding
- Similar to crawling, but smoother.
- Bacteria produce slime to slide over surfaces.
- This is called gliding movement—like a slug sliding over the ground.
➡️ 4. Sliding
- Happens when bacteria multiply.
- As new cells are formed, they push older ones forward, causing slow movement.
🎲 5. Brownian Movement
- Seen in bacteria that do not have flagella or pili.
- Movement is not controlled—it happens due to random collisions with particles in liquid.
🌀 6. Movement by Axial Filament (Spirochaetes)
- Found in spiral-shaped bacteria like spirochaetes.
- They have a special flagellum called axial filament inside the cell membrane.
- It makes the bacteria flex, spin, or creep.
- This helps them move like a corkscrew—very useful in mucus or tight spaces.