E. coli bacteria transfer genetic material through three primary mechanisms: conjugation, transformation, and transduction. These are all forms of horizontal gene transfer, meaning the transfer of genetic material between organisms that are not parent and offspring.
Conjugation
Conjugation involves the direct transfer of genetic material between two bacterial cells. This process requires cell-to-cell contact facilitated by a structure called a pilus.
- A donor cell, containing a conjugative plasmid (often the F plasmid, for fertility), extends a pilus to contact a recipient cell.
- A bridge forms between the two cells.
- The F plasmid is replicated, and a copy is transferred to the recipient cell through the bridge.
- Once the transfer is complete, the recipient cell becomes a donor cell as well.
- Conjugation can also involve the transfer of chromosomal DNA if the F plasmid has integrated into the bacterial chromosome.
Transformation
Transformation is the process where E. coli take up free DNA from their surrounding environment.
- DNA released from dead bacteria can be taken up by competent E. coli cells.
- Competence refers to the ability of a cell to take up exogenous DNA. Not all E. coli are naturally competent, but competence can be induced in the lab.
- The acquired DNA can then be incorporated into the recipient's chromosome via homologous recombination, resulting in a genetic change.
Transduction
Transduction involves the transfer of genetic material via bacteriophages (viruses that infect bacteria).
- A bacteriophage infects a bacterial cell.
- During viral replication, bacterial DNA can be mistakenly packaged into the viral capsid.
- This phage, carrying bacterial DNA, then infects another bacterial cell.
- The bacterial DNA from the first cell is injected into the second cell.
- This DNA can then be incorporated into the recipient's chromosome via homologous recombination.
In summary, E. coli employ conjugation, transformation, and transduction to share and acquire genetic material, enabling them to adapt to new environments and evolve.
