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Number of DNA entering during transformation - How many molecules of DNA are taken up during transformation (Nov/14/2007 )

Hi everyone,

Does someone knows how many molecules will be taken up by the bacteria, E.coli during transformation? Thank you very much for your opinions and information. Really appreciate it.

Best regards,



It depends on the amount of plasmid you incubate them with. I think for most cases you add a limiting amount of plasmid, so each bacteria will not incorporate more than one plasmid. Of course this is theory, and some bacteria will incorporate several plasmids.
But the amount doesn't really matter, if you're using a single plasmid to transform them - that's completely irrelevant.
If you're transforming with several plasmids (e.g. a cDNA library) and if you're aiming to get as many different transformants as possible, then you'll have to do some math, because if two plasmids are incorporated and they are incompatible, the cell will lose one of them.

Read the OD600 before you transform - that will allow you to know how many bacteria you have in your solution.
And you know the concentration of the plasmid solution you'll be using (ng/microL). If you divide that by the mass of your plasmid you'll get the number of plasmids per microL.

Then just mix the amount of plasmid you want to use with a bigger amount of bacteria - say 10^6 plasmids and 10^7 or ^8 bacteria or something like that. This way you'll know that most of your bacteria only incorporated one plasmid.

Hope this helps


It's very rare that any bacterium will contain more than one transformed plasmid. Transformation as molecular biologists do it is very inefficient. Even if you have 100 colonies on your plate, that's only 100 bacteria out of the x million available that have taken up any DNA. And there are x millions DNAs available to be taken up. With the efficiency of one bacterium taking up one plasmid being so low, the chance that one bacterium will take up two plasmids is extremely low.