Bacterial Conjugation Steps to Know for Microbiology

Bacterial conjugation is a fascinating process where one bacterium transfers genetic material to another. This exchange, facilitated by structures like the F pilus, plays a key role in genetic diversity and the spread of traits such as antibiotic resistance among bacteria.

1. Formation of F pilus

   • The F pilus is a hair-like appendage produced by F+ (donor) bacteria.
   • It is composed of pilin protein and is essential for establishing contact with recipient cells.
   • The pilus extends from the donor cell and can retract, bringing the two cells closer together.

2. Contact between donor and recipient cells

   • The F pilus attaches to specific receptors on the surface of the recipient (F-) cell.
   • This initial contact is crucial for the subsequent steps of conjugation.
   • The interaction is often mediated by surface proteins and can vary between different bacterial species.

3. Stabilization of mating pair

   • Once contact is established, the cells stabilize their connection to prevent disconnection.
   • This stabilization may involve additional surface interactions and adhesion factors.
   • A stable mating pair is necessary for the efficient transfer of genetic material.

4. Formation of conjugation bridge

   • The conjugation bridge is formed as the cells draw closer together, allowing for direct transfer of DNA.
   • This bridge is a channel through which the DNA will pass from the donor to the recipient.
   • It is essential for the physical connection required for DNA transfer.

5. Nicking of F plasmid DNA

   • The F plasmid DNA is nicked at a specific site by an enzyme called relaxase.
   • This nicking creates a single-stranded DNA molecule that can be transferred.
   • The process is crucial for initiating the transfer of genetic material.

6. Transfer of single-stranded DNA

   • The single-stranded DNA is transferred from the donor to the recipient through the conjugation bridge.
   • This transfer is typically unidirectional, meaning only one strand is sent at a time.
   • The process is facilitated by the relaxase enzyme, which helps guide the DNA through the bridge.

7. Synthesis of complementary strand

   • Once the single-stranded DNA enters the recipient cell, a complementary strand is synthesized.
   • This synthesis is carried out by the recipient's DNA polymerase.
   • The result is a double-stranded DNA molecule that is now part of the recipient's genetic material.

8. Circularization of transferred DNA

   • The transferred DNA, if it is a plasmid, will circularize within the recipient cell.
   • This circularization is important for the stability and functionality of the plasmid.
   • It allows the plasmid to replicate independently within the recipient cell.

9. Integration into recipient chromosome (if F+ donor)

   • If the donor is F+, the transferred DNA may integrate into the recipient's chromosome.
   • This integration can lead to the recipient acquiring new traits, such as antibiotic resistance.
   • The integration process is facilitated by homologous recombination.

10. Separation of donor and recipient cells

    • After the transfer is complete, the donor and recipient cells separate.
    • This separation can occur naturally as the cells grow apart or through the retraction of the pilus.
    • Both cells can now replicate and pass on the new genetic material to their progeny.