I made a bacterial transformation with an E.coli and a pCri11b plasmid that contains a GFP gene and a kanamycin resistance gene. After selection, fluorescent colonies are supposed to appear on the plate with kanamycin and IPTG, but they didn't.
I know it may be due to metabolic stress in the bacteria but I don't know what other causes there are.
It will help if you describe your transformation results more clearly. When you say "After selection, fluorescent colonies are supposed to appear on the plate with kanamycin and IPTG, but they didn't" do you mean you get (1) No/very few colonies, (2) Many colonies but no fluorescence, (3) Other?
If (1) it could be bad components, no DNA, wrong media, you didn't wait 1h after heat-shock/electroporation ...
If (2) it could be bad IPTG or wrong plasmid. If this is the case I suggest you transform and plate on LB+Kan, and only then transfer colonies to LB+Kan+IPTG.
Metabolic stress is always there but start with the simple (silly) answers...
Thank you for your response Yoram Gerchman
I decided to share a photo of my results to make it clearer.
I actually made a plate with LB+Kan, there are few colonies there, but there should be more. Then on the LB+Kan+IPTG plate you should see fluorescent colonies, due to GFP.
i do not know what went wrong with your transformatio, but efficiency is lousy (could be compatents qualit, not allowing 1h recovery, DNA quality,…). Any way, statistics of 3 colonies (in LB+K) vs 0 colonies (in LB+K+I) is meaningless, so I will suggest putting the metabolic burden idea on hold.
Instead, start by picking and plating the 3 LB+K colonies on LB+K+I, see if this solve your imidiate problem (I.e. the colonies are fluorescent with IPTG but less so without).
For the long run, debug your transformation! Take a plasmid that worked well for someone else in transformation and use low amount. Try the instructions here:
https://www.neb.com/en/faqs/0001/01/01/how-should-i-calculate-the-transformation-efficiency-c2987
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