I am using DH5 alpha recombinant cells with ampicillin resistance gene but growth of cells is very slow. I am using 50ug/ml ampicillin. what may be reason for that?
I guess you compare growth rate of transformed cells containing either an empty plamid or the plasmid encoding for you protein of interest. If so the slow growth might be due to the leaky expression of the gene on the Amp plasmid.
It took about 10-12 hours for me to get colonies on my plate, so I transformed the same plasmid with the same insert again, and this time I got a good number of colonies on ampicillin agar medium, but when I subcultured those colonies in ampicillin and kanamycin LB medium, they didn't grow, whereas I got good growth in only ampicillin medium.