Bacterial Transformation




Bacterial Transformation

Transformation is the process of introduction of derived DNA fragments from a donor bacteria into a recipient bacteria.

It is one of the cornerstone of molecular genetics.

It is the transfer of naked DNA from donor cell to recipient cell.

 

Types of transformation

  1. Natural transformation
  2. Artificial transformation

Natural transformation:

  • Most types of cell cannot take up DNA efficiently unless they have been exposed to special chemical chemical or electrical treatment to make them more permeable.
  • However, some types of bacteria are naturally transformable ie they can take DNA from environment without requiring special treatment.
  • Bacteria that take up DNA are called competent.
  • At least 40 species of naturally competent and transformable bacteria have been found.

Gram +ve : Bacillus subtilis, Streptococcus pneumonae

Gram –ve: Haemphilus infulenzae, Neisseria gonorrahe, Helicobacetr pylori, Acenetobacter baylyi, Cyanobacteria

 

Competence in Gram +ve bacteria:

Figure: competence in Bacillus subtilis

  • The protein involved in transformation of these Gram +ve bacteria is a product of com
  • In Bacillus subtilis , the com gene are organized into several operons.
  • The product of com A and com K are involved in regulation of competence and other com E, com F and com G encodes structural protein for uptake of DNA.
  • The first gene of com E operon, com EA encodes the protein that directly binds extracellulat double stranded DNA.
  • The com F gene encodes the protein that translocate DNA into cell. for example; Com FA is an ATPase that translocate DNA into cell.
  • The com G gene of comG operon encodes protein that form pseudopilus that helps to move DNA through channel.
  • The com E, com F and com G operon are under transcriptional control of com K operon.
  • Com K is a transcriptional factor that is regulated by com A
  • Some other genes involved in transformation are nuc A gene that encodes nuclease enzyme which cuts extracellular dsDNA to single stranded,
  • Single strand binding protein and Rec A gene which helps in recombination of transforming DNA with chromosome of recipient bacteria.

 

Competence in Gram-ve bacteria:

  • A variety of Gran Negative bacteria are capable of competence.
  • Some examples are Acenetobacter calcoaceticus, Helicobacter pylori, Neisseria spp, etc
  • H. pylori and Neisseria spp require specific DNA sequences for binding of DNA so these species take up DNA from same species only.

Gram-ve bacteria utilizes two different pathway for uptake of DNA

  1. PSTC transformation pathway
  2. Type IV secretion related pathway

PSTC transformation pathway

Figure: Competence in Gram negative bacteria by PSTC pathway

  • The term PSTC has been applied to some protein indicating their multiple role in Pilus formation, Secretion, Twitching motility and Competence.
  • These proteins form structure needed to transport DNA across the cell wall and cell membrane.
  • Many of these proteins that function in DNA uptake in H. influenza, Neisseria, Acinetobacter, Vibrio etc are related to com G

Type IV secretion related pathway

  • This mechanism is found in Helicobacter pylori.
  • The DNA is translocated through cell wall and membrane with the help of protein similar to Agrobacterium for conjugation of Ti plasmi.
  • Type IV system function transfer of DNA in two ways-moving in and out of cell.

 

Artificial transformation

Most of the bacteria are not natural transformable. These bacteria can be made competence by certain chemical treatment or by strong electrical shock.                                    figure: artificial transformation

Some of the methods are-

Calcium treatment:

  • Treatment with calcium ion (ca++) make same bacteria eg. E.coli, Salomenlla, pseudomonas etc competence.
  • The Calcium ion increases the permeability of cell membrane
  • Cell treated with calcium can take up both ssDNA as well as dsDNA, no matter circular or linear.

Electroporation:

  • A strong electric shock is applied in the bacterial culture mixed with naked DNA
  • The recipient bacteria should be wash with non-ionic (distilled water) solution to prevent osmotic shock.
  • The strong electric field creates artificial pore of water lined by phospholipid head group. The DNA can pass through these artificial hydrophilic pore.

References

  1. http://ars.els-cdn.com/content/image/1-s2.0-S0966842X15002474-gr1.jpg
  2. http://2014.igem.org/wiki/images/e/e8/B._subtilis_dna_uptak.jpg
  3. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC372826/
  4. https://en.wikipedia.org/wiki/Transformation_(genetics)
  5. https://www.khanacademy.org/science/biology/biotech-dna-technology/dna-cloning-tutorial/a/bacterial-transformation-selection
  6. https://www.boundless.com/microbiology/textbooks/boundless-microbiology-textbook/microbial-genetics-7/genetic-transfer-in-prokaryotes-81/bacterial-transformation-442-6842/
  7. https://www.sciencelearn.org.nz/resources/2032-bacterial-transformation
  8. https://www.ncbi.nlm.nih.gov/books/NBK21993/
  9. https://www.nature.com/subjects/bacterial-transformation
  10. http://jb.asm.org/content/196/8/1471.full.pdf
  11. https://www.jove.com/science-education/5059/bacterial-transformation-the-heat-shock-method
  12. https://www.thermofisher.com/np/en/home/life-science/cloning/cloning-learning-center/invitrogen-school-of-molecular-biology/molecular-cloning/transformation/bacterial-transformation-workflow.html
  13. http://microbeonline.com/bacterial-transformation-mechanism/
  14. http://study.com/academy/lesson/bacterial-transformation-definition-steps-analysis.html

Bacterial Transformation