Step Three: Transformation of E. coli

Once the various combinations of plasmids are made in the test tube, they are ready to be cloned. E. coli bacteria cells will do this if the DNA can be placed inside them. Because the plasmids are small it is relatively easy to introduce plasmids into bacteria. Usually bacteria are grown in large numbers and concentrated into a small volume. This concentration of bacteria can then be mixed with the plasmid DNA into a single test tube. A quick dip of the tube into a warm water bath or a quick pulse of electricity will open pores in the bacteria cells that allow the plasmids to enter the cells. The bacteria can then begin to use the plasmids like their original DNA. They will read and express the genes encoded in the plasmids and replicate them.

Fig.11: Transformation. Plasmid (A) enters bacteria (B) and adds new genetic information to create a transformed bacteria (C). (Image by D. Lee)

Fig.12: Bacteria can be transformed with a nonrecombinant (A) or a recombinant plasmid (B) or not transformed (C). (Image by D. Lee)