2. Conjugation is the transfer of genetic material between
bacterial cells of opposite mating types that are in
physical contact with each other.
A process in which DNA is transferred from a bacteria
donor cell to recipient cell by cell-to-cell contact.
3. Discovery: Joshua Lederberg & Edward Tatum
They experimented with two auxotrophic strains
of E.coli K12 denoted by Strain A and Strain B.
STRAIN A (met-bio- thr+ leu+ thi+) and STRAIN B
(met+ bio+ thr-leu- thi-) were plated on minimal
medium and incubated overnight (CONTROL), no
growth observed. Also STRAIN A and B were
mixed together and when plated on minimal
medium resulted in prototrophs.
5. The evidence for cell to cell contact was provided by
Bernard Davis (1950).
The two arms of the U tube are separated by a filter.
On the right side is medium containing auxotrophic
Strain A while on the left side is medium containing
auxotrophic Strain B.
The filter allows only the medium to move to-and-
fro but not the cells on either side.
When culture was plated from both sides on minimal
medium, no prototroph growth was observed as in
Lederberg and Tatum’s experiment.
7. Donor cell produce a pilus.
Pilus attaches to recipient cell and brings the
two cells together.
only single strand of plasmid is then
transferred to the recipient cell.
Both the cells synthesis a complementary
strand to produce double stranded circular
plasmid and also produce pilus.
Both cells are now viable donor.
9. In 1953, William Hayes determined that
genetic transfer occurred in one direction.
One cell acts as donor, and the other cell acts
as the recipient.
Cells that can donate the DNA to other cells
are F+ (male)
Cells that can receive the DNA from other
cells are F- (female).