Chapter 19 : Transformation of Escherichia coli

Abstract:

Transformation is the uptake and expression of foreign DNA by bacterial cells. Escherichia coli is one of the many bacterial strains that do not undergo transformation naturally. Transformation is thought to be an important means by which streptococci undergo genetic change, and they are undergoing genetic changes that are important to humans—they are becoming increasingly resistant to antibiotics. The cell’s DNA replication enzymes duplicate the plasmid DNA just as they duplicate the regular chromosome, so plasmid DNA molecules are inherited by both daughter cells when the bacterium divides. Scientists use plasmids as convenient vehicles for introducing new genes into cells. It is easy to isolate plasmid DNA. A vector is any DNA molecule used to deliver new genes to cells. Even the most carefully conducted transformations of E. coli are very inefficient. Scientists usually use plasmids that carry marker genes when they do recombinant DNA work. Marker genes are genes that produce an easily detected phenotype, such as resistance to an antibiotic or a color change when exposed to certain conditions.