I have to use Miniprep and Midiprep for plasmid extraction. But, I need to know what are exact differences and purposes of Mini and Midipreps other than resulting plasmid yield. And, What out of Midi and Mini prep can be used for transformation and transfection? and why?
It really is about scale. If you get enough DNA from a mini prep for your purposes, then go with that. If you need more DNA then you scale up to a midi-prep or maxiprep. All of the above can be used for transformation and transfection, assuming high quality kits/components are used.
The only difference is how much DNA you want. The more DNA you want the more bacteria you need to grow and you need different kits to produce the yield you want.
For most Miniprep Kits you bind the DNA at high salt to a silica column and the DNA is eluted in a low salt buffer or H2O.
At least the for the Midipreps we use, DNA is bound at low salt and elution is with high salt buffers. Thus, DNA has to be precipitated and washed (alternatively bound to membrane filter, washed, and eluted). In addition to the higher yield, this method results in DNA that has only low levels of endotoxins. Endotoxins can inhibit cell transfection.
If you need only a few ug of DNA for transfection experiments (protoplasts, mammalian cells), specifically look for Miniprep Kits with low endotoxin levels. The usually contain an extra wash buffer to remove endotoxins.
As others have mentioned, the main difference is scale and yield. This will also lead to difference in the mixing vessels used and how the resulting lysate is centrifuged and separated. Those two factors can affect yield AND purity.
I'd recommend using the LyseBlue reagent in your P1 buffer to ensure you are seeing equivalent mixing by visual observations. Also, refer to the QIAGEN® Plasmid Purification Handbook for specific instructions, even if you are making your own reagents or using another vendor.
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