We are assaying beta-gal fusions by replica plating to filters. We're
using this to screen a library of fusions under particular conditions. The
problem we are running into is that maybe 90% of our colonies are not blue
under the conditions we are using, consequently it is very hard to determine
which blue spot on the filter corresponds to which colony.
Does anyone know of something we can use to stain ALL the colonies on
the filter? Ninhydrin? Anything else? If we could see all the colonies it
would be much easier to pick out the blue ones. I'd like to avoid patching the
whole library or plating at a lower density if I can.