Bacterial Transformation: Mechanism

Bacterial transformation: Binding of DNA with DNA receptors

Last updated on May 20th, 2021

Bacterial transformation is one of the three horizontal gene transfer mechanisms found in bacterial cells.  The other two horizontal gene transfer mechanisms 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. DNA is released into the environment when bacterial cells (i.e. donor) die and undergo lysis
  2. Recipient cells uptake free DNA released into the environment.
  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 cells turn to ampicillin-resistant via uptake of ampicillin resistance gene through transformation. 

Bacterial transformation: Binding of DNA with DNA receptors
Bacterial transformation: Binding of DNA with DNA receptors
  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.

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

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

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

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

  • A: If the donor DNA is removed, the cell will carry ampicillin sensitive gene, but
  • B: if the donor DNA is not removed, the cell will now have an 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 cells which are successfully transformed can be selected in the laboratory by growing these cells in the medium containing ampicillin. Only resistance cells will grow.

About Acharya Tankeshwar 473 Articles
Hello, thank you for visiting my blog. I am Tankeshwar Acharya. Blogging is my passion. I am working as an Asst. Professor and Microbiologist at Department of Microbiology and Immunology, Patan Academy of Health Sciences, Nepal. If you want me to write about any posts that you found confusing/difficult, please mention in the comments below.