Hello!
I am using T7-mcherry plasmid in E. coli BL21(DE3). When I streak it on LBAmp plate, the colonies show beautiful purple-red color. When I streak it on LBAmp+0.1mM IPTG plate, the colonies becomes quite normal E. coli colonies without pink or red or purple things at all.
Then I take one purple-red colony and inoculate an overnight culture in LB Amp culture, the overnight culture did not show any red color. However, when I take one normal colony (from LBAmp+0.1mM IPTG plate) and inoculate an overnight culture in LB Amp culture too, the overnight culture show pink color. I am so confusing about this. Does anyone know the reason for this? THanks!
It may be that with high level expression the protein forms inclusion bodies and/or doesn't fold correctly. But you get nicely folded protein when at low expression levels. It could also be that when you pick colonies from an IPTG plate you have selected for mutants that don't express. Induced expression might be toxic
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