Plasmid Prep II

[Obaid Yusuf Khan]

I am having a problem with my plasmid preps which is sort of similar to the 
"Plasmid Prep" thread of this group.

I am growing up pBR322 based plasmids in 100mcg/ml Amp in Luria Broth, but 
getting very low amount of plasmid back. The o/n culture density is OK, but it 
seems that lot of bugs do not contain the plasmid. I used fresh Amp and the 
results were somewhat better. Then I tried using 150mcg/ml of Amp in LB which 
showed further improvement on plasmid yield. One thing I noticed when growing 
the bugs on plates is that I get more satelite colonies than I usually use to have. I 
am using Amp from SIGMA and have used the same product for the past 4-5 
years without any problem.

I wonder if anyone has had some similar problems. I will appreciate any 
comments. Thanks very much

Obaid Khan