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Bacterial conjugation

bacterial conjugation genetic transfer transfer of genetic material in bacteria F+ and F- factors bacterial biology genetics factors in bacterial genes genetics DNA synthesis mobilization cell to cell contact bridge formation

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Bacterial conjugation

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  3. 3. HISTORY J. Lederberg and E. Tatum demonstrated the transfer of genes between bacteria that depends on – direct cell to cell contact mediated by the F pilus – unidirectional DNA transfer from donor to recipient Bacterial Conjugation
  4. 4. Bacterial Conjugation Bacterial conjugation is the transfer of genetic material between bacterial cells by direct cell-to-cell contact or by bridge-like connections between two cells.  The genetic information is often beneficial to the recipient.  Exchange of genetic material b/w bacteria  Physical contact required  DNA exchanged via Pilli  Drug resistance!!  Horizontal Gene Transfer
  5. 5. TERMINOLOGY 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- cells
  6. 6. Bacterial Plasmids • Small, autonomously replicating DNA molecules – can exist independently from host chromosome – can integrate reversibly into the host chromosome (episomes) • Conjugative plasmids (F plasmid) can transfer copies of themselves to other bacteria during conjugation
  7. 7. 15 • F factors contain the information for formation of sex pilus – attach F+ cell to F- cell for DNA transfer during bacterial conjugation • F factors have insertion sequences (IS) – assists in plasmid integration Bacterial Plasmids - 2
  8. 8. 1- Cell – Cell contact Formation of “sex pilus” or F-bridge between cells Attachment Via Pilli
  9. 9. 2- MOBILIZATION  Target DNA is replicated in F+  Genetic transfer of ssDNA to F- Genetic Transfer of ssDNA
  10. 10. F+ x F- Mating • A copy of the F factor is transferred to the recipient and does not integrate into the host chromosome • Donor genes usually not transferred • F factor codes for sex pilus – Type IV secretion system that makes contact between cells that DNA moves across • Plasmid is replicated by rolling circle method
  11. 11. HFr Conjugation • Donor HFr cell has F factor integrated into its chromosome • Donor genes are transferred to recipient cell • A complete copy of the F factor is usually not transferred • Gene transfer can be clockwise or counterclockwise
  12. 12. 3- DNA SYNTHESIS  Complementary strands of DNA are replicated in both F- and F+  Target DNA is incorporated into F- genome Synthesis of complimentary DNA
  13. 13. 4- SEPARATION  Cells separate  Form two F+ cells with completed recombinant plasmids  Both serve as donor cells for further conjugation Separation and formation of two F+ cells
  14. 14. F’ Conjugation • Result when the F factor incorrectly leaves the host chromosome • Some of the F factor is left behind in the host chromosome • Some host genes have been removed along with some of the F factor – these genes can be transferred to a second host cell by conjugation
  15. 15. Thanks hafsaranjha.botanist@gmail.com