Bacterial Transformation: Mechanism

Bacterial Transformation is one of the three horizontal gene transfer mechanism found in Bacterial cells.  The other two horizontal gene transfer mechanism are conjugation (Transfer of F Plasmid & Transfer of Chromosomal DNA)  and transduction (Generalized Transduction & Specialized Transduction).

Bacterial Transformation
Bacterial Transformation

Key information regarding bacterial transformation

  1. Recipient cell uptake free DNA released into the environment.
  2. DNA is released it to the environment when another bacterial cell (i.e. donor) dies and undergoes lysis
  3. Not all bacteria are capable of taking free DNA from the environment, Only competent bacteria can do. Those bacteria that are  able to take free DNA and are able to go transformation are called competent bacteria.

Some example of Pathogenic bacteria showing competence

  • Haemophilus spp
  • Streptococcus spp
  • Neisseria spp

Mechanism of Bacterial Transformation:

In this particular example, we are going to observe how  Ampicillin sensitive bacterial cell turns to Ampicillin resistant via uptake of ampicillin resistance gene through transformation. 

  1.  Competent bacteria have DNA receptors in the surface of its cell. Free DNA which is available in the vicinity of those bacteria can bind to the DNA receptors.
  2. Double stranded donor DNA binds to specific receptors on the surface of competent cell.
Bacterial transformation: Binding of DNA with DNA receptors
Bacterial transformation: Binding of DNA with DNA receptors

3. Only single strand of donor DNA reaches to the interior of the recipient cell, the other strand get degraded by nuclease.

4. Recombination with the recipient’s homologous DNA occurs.



Bacterial Transformation: Entry of donor DNA
Bacterial Transformation: Entry of donor DNA

5. Mismatch repair system of DNA comes into play and it either removes donor DNA or recipient DNA.

6.If the donor DNA is removed, the cell will carry Ampicillin sensitive gene, but if the donor DNA is not removed, the cell will now have Ampicillin resistance gene.

Selecting transformed bacterial cells.
Selecting transformed bacterial cells.

so in a mixture of cells some cells contain the new donor DNA and others have the original DNA sequences.
Bacterial cell which are successfully transformed can be selected in the laboratory by growing these cells in the medium containing Ampicillin. Only resistance cells will grow.



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