My work is stock on a trouble for plasmid isolation. Could any one give me some suggestion or comment? I cloned one DNA into vector, after transformation, the negative control was clear, no bacteria grew.The positive control grew very well, and my experimental group grew about 40 clonies in one plate. But when I did miniprep of plasmid by QIAGEN kit, I could not get any plasmid. What happened? Thank you in advanced!