Transformation Efficiency

Hannes Klump klump at
Sun Apr 11 15:31:42 EST 1999

Dr Antony Halsall wrote:

> Hi all,
> I am transforming CaCl competent cells and would be grateful if anyone could tell me, or
> point me in the right direction on, how to calculate the transformation efficiency of my
> cells. I am/may be foced to blunt end ligate and therefore want cells with a high
> transformation efficiency. Our copy of Current Protocols in Molecular Biology is missing
> the vital pages.
> Thanks for any help
> Dr Antony Halsall
> Dept Psychological Medicine


To calculate the transformation efficiency of your competent bacteria (from which you should
also know the number of cells/volume), you have to do a control transformation first with a
plasmid of known concentration.
Counting the number of colonies next day tells you how competent your cells are; for
you get 100 colonies after transformation with 1 ng plasmid.
This means that you can expect 10 to the 5th (100 colonies * 1000ng plasmid) transformed
bacteria per microgram plasmid.
That´s the usual way the term "competence of bacteria" is used ( = how many transformed
bacteria can I expect after putting 1ug of DNA into them?)

Best wishes,

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