In pretty much every transformation protocol I\'ve seen SOC medium is used to gr
ID: 30702 • Letter: I
Question
In pretty much every transformation protocol I've seen SOC medium is used to grow the bacteria for a short while after the tranformation and before plating.
I've usually substituted LB medium for this step for easy retransformations, but I gather that the SOC medium is supposed to make some difference in efficiency, or else the simpler LB medium would be recommended in the protocols.
Why is SOC medium used for transformations? What difference does substituting with LB medium cause for the transformation efficiency?
Explanation / Answer
To summarize from Hanahan's paper (see below for reference), he carried out a systematic review of conditions necessary to improve transfection efficiency. Among the conditions tested were the presence of various cations (Ca2+, Cs+, Mn2+, K+, Mg2+), DMSO, and growth temperatures (and a few other conditions not so commonly used these days). He worked with a strain that he subsequently isolated a derivative of, called DH1, which is now available commercially as DH1-alpha and other strain derivatives.
He defined transformation efficiency to be the number of transformed colonies on a plate, a measurement still used today. He found when the transforming media contained: certain cations, specifcally Mn2+, Ca2+, Rb+; as well as DTT, hexamine cobalt (III) and DMSO; greatly improved the transfection efficiency compared to the standard Ca2+ treatment. He also found that sucrose and K+ were useful, though not strictly necessary for his experimental strain. It was stated in this paper, though not explained, that sucrose acted as a stabilizer, possibly to guard against his initial use of 0