Of all the model organisms profiled in this unit, Escherichia coli, commonly called E. coli, may be the best understood. Dr. Theodor Escherich (1857–1911) discovered this normal resident of the human intestinal tract in 1885, and it quickly became a popular lab organism. Biologists have studied every aspect of this bacterium for over a century, and its contributions to biology are enormous. The following are a few highlights:
DNA is genetic material
In 1950, Hershey and Chase used virus-infected E. coli cells to demonstrate that DNA, not protein, is the genetic material. Genetic exchange: In the 1940s and 1950s, biologists studying E. coli discovered conjugation and transduction. Both phenomena have important implications for bacterial evolution and transgenic technology.
In the late 1950s, Matthew Meselson and Franklin Stahl used E. coli in their famous experiments that demonstrated how DNA is copied.
The 1961 description of the lac operon in E. coli revealed how cells can turn genes on or off, depending on environmental conditions such as the type of sugar present.
In 1973, E. coli became the first organism to receive a gene from another species. The researchers used the newly discovered restriction enzyme EcoR1, derived from E. coli, to produce the recombinant plasmids. Since then, E. coli cells have received countless genes from many other species.
The E. coli genome has been sequenced, and many scientists are working to describe the functions of hundreds of E. coli genes. Many genes in other organisms, including humans, will no doubt have similar DNA sequences and functions. Such studies of homologous genes yield new insights into disease and cell function.