Fingering and Branching Patterns by Bacteria

The patterns you see in the pictures above are formed by bacteria as they grow on a plate of agar. Agar is somewhat like jello, and is used as gelling agent in many foods. As in other experiments, the bacterial growth was started from the center of the agar. The agar is in a dish about 4 inches across. The depth of the agar is about 1/10-th of an inch.

At first the bacteria grow densely outwards. However, the agar has been deliberately made so that there is an insufficient concentration of nutrients for the bacteria to feed as rapidly as they grow.

Can you relate the nutrients in the agar to a quantity in the metal deposition experiment?

Do you see a similarity to the fingers formed by the bacteria and the fingers you observed in the liquid fingering experiment?

What is your image of how the bacteria are behaving?

Many of these bacteria experiments are done using Bacillus subtilis or Escherichia coli.

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