BIOLOGY Volume 3 - A Guide to General Biology - 2004

25. APPLIED GENETICS

25.1. Bacterial Genetic Engineering

25.1.4. Step 3. Introduction of the Vector into the Host Cell

At this stage, the phage or plasmid vector is introduced into a bacterial Cell where it can replicate (cloning both itself and the foreign donor DNA it carries). Typically, the bacterium Escherichia coli—a common inhabitant of the human gut—is used for this purpose. E. coli is chosen because its genetics are thoroughly understood and it grows rapidly, with a doubling time of about 30 minutes. For Introduction/32.html">Genetic Engineering purposes, a special mutant strain of E. coli has been developed that survives only under specific laboratory conditions. As a result, it cannot infect humans if accidentally released into the environment along with the foreign genes it contains.

When using a plasmid vector, the plasmid preparation is added to a test tube containing an E. coli culture. Calcium Ions (typically as calcium chloride) are also added, and the Cells are subjected to a brief heat Shock. This rapidly induces Pores in the E. coli cell membrane through which Plasmids enter The Cell. The process of introducing new DNA into a bacterial cell is known as transformation.

Phage vectors are introduced into cells by infecting a bacterial lawn growing on Agar plates (Section 12.8).