MadSci Network: Molecular Biology

Re: Why will transformed bacteria only contain one type of construct?

Date: Thu Jun 4 03:13:44 2009
Posted By: Sebastien De Landtsheer, Undergraduate, Immunology, Laboratoire National de Santé
Area of science: Molecular Biology
ID: 1244037145.Mb

Hello Tina,

The transformation efficiency, even with a nice plasmid and E. coli in good shape, is very small. Actually, most of the plasmid stays in solution and most of the bacteria remain non- transformed.

Let's use numbers, even if they might be wrong. Your have say, 109 input bacteria, and you end up the next day with about 100 colonies. So a single bug has about one chance in 107 to catch a plasmid molecule. So that's one chance in 1014 to catch two at the same time.

In other words, each of your resistant colonies has a chance in 107 to have a second plasmid. On every plate you have one chance in 10,000 to have a double-transformed bug.

[Not all of those double-transformants will be transformed with both an inserted-vector and a religand, so the chance of observing the particular double-transformant in question will be even lower, depending on the ratio of inserted to religanded vectors. -SM, Moderator]

Hope that helps!

Good luck with ongoing experiments.


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