Hi Ganesh, you can pellet bacteria, remove all medium and store the pellets at -20°C for months, for both protein expression or plasmid DNA extraction.
Thank you for the answers.
Actually, I had stored the pellet with minimum quantity of medium for 4 days and then when I used this pellet to isolate plasmid, even though I got traces of nucleic acid readings in nanodrop measurements (~12ng/uL), I could not spot any DNA on 0.8% agarose gel. What might have gone wrong?
PS: I had used Qiagen kit for isolation.
Different things could have gone wrong...
You might not get plasmid DNA because the culture did not grow enough, or your plasmid is low copy so you would need larger miniprep inoculation to extract DNA, or DNA was not efficiently recovered from the column (mostly if it is a large plasmid, which the use of a 0.8% gel makes me think...) or, finally, it could have degraded at 4 °C: cells at 4 °C slow down significantly their metabolism, but are not completely arrested, and slowly die and degrade all their content... in fact even on agar after about 1 month at 4°C the cells (clones) are dead and you can't regrow them and would extract nothing...
If you don't have time to process minipreps on the day best is to pellet, remove all medium and freeze. They will thaw very quickly in resuspension buffer when you wish to process them...
Good luck.
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