Is there a cheaper alternative to IPTG?

Song Tan tan at
Thu Dec 8 09:54:10 EST 1994

In article <3c30sr$9ss at>,
rsaldanh at (Roland J Saldanha) wrote:

> In article <Pine.SUN.3.90.941206162348.23020A-100000 at condor>,

> > I am trying to induce moderate quantities (about 5 liter cultures) of an
> >E. coli strain with a plasmid containing a gene controled by the lac
> >promotor. I dont want to finish our next year supply of IPTG and I would
> >like to ask if anyone knows about a cheaper alternative of lac induction.

> I regularly use Lactose! for strains that  are lac plus (DH5 alpha will not be
> since it is designed for alpha complementation and your insert presumbaly
> inactivates the alpha fragment of lacZ if you are using common vectors).  You
> could move your construct to any lac plus strain and do the same.
> Lactose is about $5 for a pound and we use 0.2% to induce (10 mls of a 20%
> solution / liter).
> I use BL21 a strain designed for T7 based constructs.

Someone in our lab tried unsuccessfully to use lactose instead of IPTG for
induction a while ago and decided the problem was pH changes as the
lactose was hydrolyzed by the cells.  IPTG doesn't suffer from this
problem because it is nonhydrolyzable, of course.  

Still, I've love to hear if others have been successful in replacing IPTG
with lactose.

Song Tan
Institute for Molecular Biology and Biophysics
ETH-Honggerberg (Swiss Federal Institute of Technology)
8093 Zurich, Switzerland
email:  tan at

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