Do bacteria collide with each other while swimming?

On a hot day in a busy swimming pool, I am often clumsily found paddling my way bumping into people. So it’s obvious to ask – do bacteria swimming around in water collide with each other.

This is not such a simple question after all. Offcourse it should depend on how many bacteria are present per unit volume? What kind of bacteria (swimmers or gliders that stick to surfaces). But I want to share an observation that makes me begin to think that individual bacteria might have either passive or active “self-avoidance” mechanisms based on the hydrodynamic theory of images.

Watch the movie – and you can spot a few collisions; but not as many as my intuition tells me.

In the next few posts, I will teach how to track individual swimming organisms (using imageJ and flowtrace); and discuss the theoretical ideas behind collision (borrowing from kinetic theory of gases).

For right now; enjoy this soup of bacteria.

If you are curious how I collected this data – see my previous posts on how to image bacteria. This is a simple darkfield illumination setup just using a tilted table lamp as the light source.

See and

And many other posts from the past!



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