PEG and DMSO in bacterial transformation

Ludla ludla at
Sun Apr 20 14:46:04 EST 1997

Susan Walsh posted the following:

>I received a protocol for bacterial transformation.  The solution >used
for competence contained polyethylene glycol and dimethyl >sulfoxide.  I
was wondering if anyone knows why these reagents >are included in the
protocol.  What do they do to enhance >competence and transformation?
>Thank you,
>Susan Walsh
>sjwalsh at

Many yrs. ago I produced monoclonal antibodies..... fusion of the
malignant cell line with the chosen cells REQUIRES polyethylene glycol....
reason given in lit (that I can not find anymore! Sorry!) is that PEG
"mimicks" membrane lipids and substitutes into the cell membranes by
concentration differences.  Once enough PEG is susbstituted into the
membranes, fusion of membranes is basically due to "likeness", i.e., the
membranes have a high percent PEG.  Presumably also occurs in nuclear
membranes (although you don't have to worry about that with bacteria!).

DMSO is a very strong solvent..... and also has the ability to pass
through membranes as if they don't exist!  (Be VERY careful when using
DMSO-dissolved compounds - will function on YOU, too.)

Presumbaly the use of both PEG and DMSO in transformation of bacteria is
to effectively increase permeability of the cells, and at the same time
supplying a solvent system which carries the DNA through without damage
(DMSO is also used in PCR of recalcitrant DNA/RNA, apparently by lowering
Tm and reducing secondary structure.  May also help in passage across
membranes in much the same way.)

Hope this helps!

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