The propagation (cloning) of a recombined plasmid cannot occur in
vitro. As a consequence, the bacterium Escherichia coli
is commonly used for this process. The reasons this cell is ideal
E. coli has a single chromosome containing ~5 million base pairs
(only 1/600th the size of a haploid human chromosome).
this organism in a normal component of the gastrointestinal flora of mammals,
and can be cultured easily and inexpensively.
since the genetic code is composed of only four bases (A,T,C,G) any foreign
DNA inserted into the chromosome of E. coli is treated as a natural
component of its chromosome and replicated normally.
transformation of E. coli is easily accomplished.
Bacterial Population Growth in a Closed Environment (Batch Culture)
this bacterial species replicates under ideal conditions once every 22
minutes, so large populations of transformed cells are produced in just
a few hours.
1. Lag Phase - cells first introduced;
adjust to the environment.
2. Log Phase - cells reproduce exponentially.
3. Stationary Phase - cells reach the
upper limit of population growth.
4. Decline Phase - cell population declines
exponentially as resources are