Expansion of commercial competent bacterial cell lines? - (Nov/14/2013 )

Is it possible to thaw out a competent cell line (e.g. JM109), expand it out in normal LB (without antibiotics) and refreeze it back in glycerol?

Will these cells loose their competency?

My question arose because I needed more cells because I have increased the number of plasmids to transform.

Yes, you can safely prepare your own competent cells from most commercial ones (including JM109), e.g. by using the CaCl2 method for preparation of chemically competent cells. We constantly do this in our lab with BL21DE3, DH10Bac, Dh5alpha, ...

The efficiency of transformation of calcium chloride prepared cells will be 2-3 orders of magnitude lower than commercial cells. If you want to prepare high competency cells, you can do it with a protocol such as this:

http://openwetware.org/wiki/TOP10_chemically_competent_cells