Glycerol vs. Glucose in bacterial media

Duncan Clark Duncan at
Fri Dec 16 11:51:27 EST 1994

In article: <3cptjk$qib at>  rgs at (Robert Solomon (Bioc)) writes:

> ca. 30 mM.  But I have not observed much difference in expression/yield
> from strains grown at different times with either carbon source. 
> Obviously, if using a catabolite promoter (e.g. lac promoter) then
> it's best to avoid glucose, but this is not the case for tac promoter,
> and I can't see why it should be for lambda pL or pR promoters. 
> Ignorance is such bliss.

Glucose should repress the tac promoter as much as the lac promoter. 
The only difference (apart from the -35 region) between the promoters
is their strength. They both have the lac operator sequence and should
therefore behave the same as regards glucose.

The main problem with glucose in the media is the formation of acetate
which in unbuffered media causes a substantial drop in pH. Buffering 
with phosphate helps as does controlling the growth rate by glucose 
feeding rather than just putting in all the glucose at once.

My mind's made up. Don't confuse me with the facts!

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