Need ideas for Lac+/- screening in Neisseria

Hank Seifert h-seifert at
Thu Jul 27 10:48:12 EST 1995

We are attempting a screen for constiutive regulatory mutants that allow 
expression of a gene fused to a LacZ reporter in the genome of the 
gonococcus.  The bacterial colonies grow fine on Xgal unless they express
the LacZ. Then they growth slowly and are hard to recover.
We presume the indole derivative cleaved from the Xgal by betea-gal 
is toxic for the bugs. This is a real problem since
we are selecting against the mutations we want. We are trying the other beta-gal substrates magenta-gal and rose-gal but 
think that the similarity to the Xgal may produce the same problem.

Does anyone have other screens for beta-gal activity that can be done on
a solid medium? 

Thanks for the ideas and please email a copy of any responses to me.

Hank Seifert <h-seifert at>
Associate Professor
Department of Microbiology-Immunology
Searle 6-467, Maildrop W213
Northwestern University
303 East Chicago Ave.
Chicago, IL 60611
Tel: (312) 503-9788
Fax: (312) 503-9787 or -1339

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