help needed on library screening

[suisheng at sfu.ca]

 Hi, netters:
 I have a question about a cDNA library screen. I don't know why there
 are a few big round(2-4 mm diameter) clear plaques among those normal
 size plaques in the plates. I tried both SURE and XL1-blue as a host,
 Uni-ZAP XR phage as a vecter. In 150 mm plate I added both 25,000 and
 50,000 pfu with 600 ul host which O.D.600 = 0.5. I did a few times
 and can't get rid of those big clear plaqures. I still wonder wether
 these big plaques have any affect to my screening and why it happen?
 Dose anyone out there have these experience? Any suggestion is
 welcome.
 
 Thank you for your attention.
 
Suisheng Tang

suisheng at sfu.ca