GUS assays in E. coli

[JON BOXALL.]

Hi,
	I'm looking for a strain of E.coli that I can use for selection
of beta-glucuronidase (GUS) positives.  The strain I'm using at the moment
is XL-1, and I find that the background glucuronidase activity in this strain
is rather high, causing false positives, and a very low signal to noise ratio.
Can anybody recommend a strain with low endogenous glucuronidase activity that
I might switch to?
	Thanks,

		Jon Boxall.