Hello everyone,
I did a transformation of E. coli DH10B using pUC18 plasmid. The bacterias did grow on MKL medium with ampicillin but the colonies showed a white/pink colour and the medium was completely yellow. Usually, when these bacterias are transformed they grow on MKL+ampicilin medium but present a purple colour and the medium is also red/purple.
I will be very grateful if someone knows why this could happen.
Thank you so much for your help.
Pamela B
I presume MKL is MacConkey Lactose? I actually would not expect DH10B wiht pUC18 to be Lac+ or red on MacConkey plates (it is only weakly lac+ which you can see easily with Xgal but does not really ferment lactose at an appreciable rate). The all yellow color indicates a Lac- strain. But if the strain is not behaving in your hands like it normally does, then it would seem either you have a contaminant or something is wrong with your plasmid.
Those are definitely possibilities. Another might be that the ampicillin in the plates went bad and there's untransformed background colonies, maybe some of which are spontaneous mutants resistant to low levels of amp. Low salt LB amp 100 µg/mL plates are only good for about a month when stored at 4°, in my experience.
- Badges
- Science topic