How to get rid of excess lactose in media?

Michael Oda MNODA at
Wed Aug 27 13:53:32 EST 1997


     Our lab has been expressing some human proteins in coli, which happen
to be somewhat toxic to the cell. Things were going along fine and expression
levels were good. Suddenly the cells stopped expressing or even growing
in enriched media. We had checked everything from water to the glassware.
Because we are using the pET expression system (with pLysS), we are vulnerable
to lactose in the media, which would induce T7 RNA pol synthesis. After a
month of eliminating potential causes, we narrowed our problems down to
the media, specifically the bacto tryptone, which apparently contained
a significantly higher than normal quantity of lactose. After this long
set up my question is: Is there a way to remove this excess lactose from our
media or are we forced to buy multiple lots of bacto tryptone and use the
one with the least lactose?:) Better yet does anyone know of a lot #
of bacto tryptone that has low levels of lactose? I had considered adding
filtered B-galactosidase to the media until I saw the price of the enzyme. 

                              Thanks in advance,
                              Mike Oda

Michael Oda, PhD.                      |   Phone: (510) 486-4088
Donner Labs                            |    Fax: (510) 486-4750
Lawrence Berkeley National Laboratory  |  Pager: (510) 702-4427 
Berkeley, CA  94720                    |  email: mnoda at

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