The initial evidence for bacterial conjugation,the transfer of genetic information by direct cell to cell contact, came from an elegant experiment performed by Joshua Lederberg and Edward L.
Tatum in 1946. They mixed two auxotrophic strains, incubated
the culture for several hours in nutrient medium, and then plated
it on minimal medium. To reduce the chance that their results
were due to simple reversion, they used double and triple auxotrophs on the assumption that two or three reversions would not
often occur simultaneously.
Lederberg and Tatum did not directly prove that physical
contact of the cells was necessary for gene transfer. This evidence was provided by Bernard Davis (1950), who constructed
a U tube consisting of two pieces of curved glass tubing fused
at the base to form a U shape with a fritted glass filter between
the halves. The filter allows the passage of media but not bacteria. The U tube was filled with n…