Conjugation
Some strains of E. coli possess a plasmid (the F’ factor) that allows them to transfer DNA to a recipient of the similar species. The transfer of DNA is unidirectional from the donor carrying the F’ factor (the strain designated F⁺) to a recipient (F^-) that does not have the plasmid. The copying of the F’ factor plasmid is accompanied through a physical joining of donor and recipient via a plasmid-encoded structure, the F-pilus. After conjugation is complete the recipient becomes F⁺.

Conjugation was first described in year 1946 by Lederberg and Tatum who noted that two Bacterial auxotrophs could be mixed together to make a new nonauxotrophic strain. They  noted that the  transfer of information could be  stopped easily  through  shaking the cells  even  though the  shaking process did  not  kill the cells outright. Others separated the donor and recipient by a fine filter and demonstrated that physical contact between the cells was an absolute requirement for conjugation. The process was not fully understood until it became apparent that the strains that could act as donors (high- frequency recombination or Hfr strains) all possessed the large F’ plasmid. It was also shown that F’ could integrate into the genome of the Hfr strains. During the procedure parts of the donor’s chromosome may be copied and transferred as well while rarely the entire complement. If the acquisition of the donor’s DNA causes the recipient to change its phenotype after recombination the recipient is said to be a transconjugant.