The plasmid preparation generally involves the growth of the bacterial culture. Plasmids are mainly purified from liquid bacterial cultures such as E.coli which have been both isolated as well as transformed. All the plasmid vectors virtually encode 1 or more that antibiotic resistance genes as a selectable marker. Bacteria possessing a gene encoding kanamycin or ampicillin resistance helps them to multiply uninhibited.
In plasmid preparation service is a bacteria which has not taken up the plasmid vector are known to lack the resistance gene. So, only those colonies which have represented successful transformations are expected to grow, and that too under favorable conditions. Whenever the bacteria are lysed under alkaline conditions, then the denaturation of both chromosomal DNA, as well as protein, occurs. But, in this case, the plasmid DNA remains stable.