I did the 2nd round amplification of M13 phage containing two control proteins

A.Streptavidin

B.N-acetyltransferases

1. After the phage titration i was not able to see any blue plaque on IPTG/X-gal plates,but i can see the clear white color zone of inhibition on plate(plaques)

2. But the plates including IPTG/X-gal which i made was fresh and the concentration is also same.

3. When I had followed the same things as above mentioned I have seen the blue plaques, just one week before.

4.As a control plate already known concentration of phage being used,in this control plate could see the lawn of plaques.

5. I have repeated the experiment 4 times but same type of result i am seeing

   Plz help me to figure it out the problem and make me to understand where i am doing any thing wrong or not following proper steps.

Thank you,

D.Rajashekar.