Chapter 20 : Conjugation

Abstract:

In 1946, Joshua Lederburg and Edward Tatum discovered that genes could be exchanged between Escherichia coli cells in a process that required direct contact between the cells and a special fertility (F) factor in the donor cell. This process was named conjugation, and it is also referred to as bacterial sexuality because of the direct donation of genetic material. The basic form of the F factor is the F plasmid, a very large plasmid that contains several genes required for its conjugational transfer. Any cell that contains the F plasmid can synthesize all the proteins needed for conjugation (from the F genes) and so is "fertile." Fertile cells synthesize a special structure called a pilus, a tubelike appendage that protrudes from the outer membrane. The F plasmid occasionally recombines into the E. coli chromosome. It is believed that conjugation is the most important route of transmission of antibiotic resistance in most disease-causing bacteria. In this activity, students will observe the conjugative transmission of ampicillin resistance to a cell that is already resistant to streptomycin. The antibiotic streptomycin acts by binding to a ribosomal protein and preventing protein synthesis.