Conjugation is the transfer of genetic material between bacteria through direct cell-to-cell contact. Joshua Lederberg and Edward Tatum discovered conjugation in 1946 while experimenting with two auxotrophic E. coli strains - strain A could produce certain amino acids while strain B was deficient in those amino acids. When mixed together, prototrophic bacteria emerged that could produce all amino acids. Further experiments showed conjugation requires physical contact between cells. During conjugation, the F plasmid containing the genetic material is replicated in the donor cell and transferred to the recipient cell through a sex pilus. The recipient cell then incorporates the new genetic material into its genome. This allows for the exchange of genetic information between bacterial cells.

2. Conjugation
Subhananthini jeyamurugan
18PY17
I M.Sc., Microbiology
ANJA college , Sivakasi.

3. Transfer of
Genetic material
from Bacteria A
to Bacteria B by
Matting or
contact is called
conjugation.
What is conjugation?

4. History
 Discovery: Joshua Leaderberg & Edward Tatum in
1946.
 They experimented with two Auxotropic strain of
E.coli K12 denoted by Strain A and Strain B.
 Strain A ( met- bio- thr+ leu+ thi+) 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.

6. Conjugation requires physical contact
• The evidence for cell to cell contact was provides by Bernard
Davis in 1950.
• The to 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 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.

8. Who is donor?

9. Terminology
HFR ( F+) ( F-) Mixed culture
♪ The donor
♪ F+
Fertility
Factor
♪ Contains
genetic
material for
gene exchange
‘Male’ cell.
♪ The recipient
♪ F-
No fertility
factor
♪ Receives
genetic
material
‘Female’ cell.
♪ The conjugate
♪ HFR
High frequency
recombinant
♪ Resulting genetic
recombinant
♪ Transfers entire
genomic DNA
when mixed with
F-

10. What happens during conjugation?

11. What is HFR cell?
When F factor/ plasmid exists in an integrated
state with the host chromosome.

12. HFR conjugation

13. Stages during conjugation
1. cell to cell contact
2. Mobilization
3. DNA synthesis
4. Separation

14. 1. cell to cell contact
Formation of “sex pilus” or F- bridge between cells.

15. 2. Mobilization
• Target DNA is replicated in F+
• Genetic transfer of ssDNA to F-

16. 3. DNA synthesis
• complementary strands of DNA are replicates in both
F+ and F- cells.
• Targeted DNA incorporated into F- genome.

17. 4. Separation
• Cells separate.
• Form two F+ cells with complete recombinant plasmids
• Both severe as donor cells for further conjugation.

18. Bacterial conjugation
in E.coli strains
HFR ( F+) ( F-) Mixed culture
 Able to produce
amino acids
Thr, Leu, Thi
 Sensitive to
Streptomycin
 HFR strain used
for experimental
purposes
 Requires amino
acids
Thr, Leu, Thi
 Resistant to
streptomycin.
 Able to produce
Thr and Leu
 Thi not produce
 Resistant to
streptomycin