E.coli Compotent Cell Storage and Plasmid Isolation - (Jul/23/2007 )

Hello,

E.coli compotent cells JM109E were stored at -50C. Upon transformation, cells grew on plates. Single colony was used for LB broth. Broth culture grew somewhat and a QC plate grew plate grew very well.
However, no plasmid was isolated in subsequent steps. Could the compotent cells have lost their efficiency?

Thanks

I'd check the antibiotic first. Was it stored correctly? Maybe try it with a new batch. Many things can go wrong at the plasmid isolation, too (although it is less likely, if you do it routinely).

I agree with Kupac, maybe your antibiotic has gone bad. Try not to thaw/freeze too many times.
If that's not the problem I say try a transformation with a vector like pUC (with know concentration) to assess the competence of your cells.