conjugation

bacterial transformation

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

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

3. 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 .

4. 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.

5. Who is donor?

6. 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-

7. What happens during conjugation?

8. W hat is HFR cell? When F factor/ plasmid exists in an integrated state with the host chromosome.

9. HFR conjugation

10. Stages during conjugation cell to cell contact Mobilization DNA synthesis Separation

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

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

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

14. 4. Separation Cells separate. Form two F+ cells with complete recombinant plasmids Both severe as donor cells f or further conjugation.

15. B acterial 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