Blue/white selection - More color at lower temp (Oct/05/2005 )

Does anyone know why the blue color of a colony growing in a Xgal/IPTG selection plaque intensifies when the plaque is placed in the fridge for a couple of hours? Thanks!

You know, this is one of those things that I've always done, but never bothered to figure out why it works...

I'll be interested if anyone has a theory or answer to this...

not sure but assuming bacterias still grow at 4°, that allows intensification of blue colonies?...

Yes, bacteria still grow at 4°C, but obviously much slower than at 37°C. But, if you take two plates that have blue colonies on them after overnight growth at 37°C, and remove one plate to 4°C for several hours, the blue colonies on the refrigerated plate will be much more intense than those on the plate left at 37°C...

Perhaps bacteria in stationary phase are going to produce more B-galactosidase since they are not investing as much energy into reproduction. Just a theory....

Agree with that theory

Yep -- that one has the ring of truth about it. Nice one, tap14!