A lawn of E. coli stained with Coomassie Brilliant Blue dye.

Last year I found myself needing to visualize growth of a relatively thin lawn of E. coli on imperfectly translucent minimal medium plates. It was part of testing growth based on our predictions in the recently published Computing minimal nutrient sets from metabolic networks via linear constraint solving (I’ll have a separate post about that soon). Trying to get the lawns to stand out via backlighting or dark backgrounds didn’t do the trick, but staining the cells finally gave me the lovely picture you see above.

The protocol I used came from this page at the Center for Polymer Studies at Boston University.

Protocol: How to coomassie stain a bacterial plate

First, make staining solution.

1 liter staining solution:

1) To 400 mL distilled water, add 500 mL methanol
2) Add 100 mL acetic acid
3) Add 1 gram 0.1% Coomassie Brilliant R stain powder
4) Mix until the solution is a uniform blue

1 liter rinse solution:

1) To 400 mL distilled water, add 500 mL methanol
2) Add 100 mL acetic acid

(In other words, the staining solution minus the stain.)

To stain your bugs:

1) Pour the staining solution onto the plate so that it just covers the surface of the agar.
2) Let stand for 45 seconds.
3) Pour off the solution.
4) Pour on the rinse solution.
5) Swirl it for 10 seconds, then let stands for another 50 seconds.
6) Pour off the rinse solution.

It’s easy, and the resulting plates are quite pretty.