Bacterial Transformation Definition

Bacterial transformation is the absorption and frequent expression of a newly acquired trait in a recipient bacteria as a result of the passage of free DNA from a donor bacterium to the extracellular surroundings.

• This procedure simply needs free DNA in the environment and does not need a live donor cell.
• The transformant is the recipient who propagates the new DNA.
• During extreme climatic conditions, several bacterial species transfer DNA from their cells into the environment for competent cells to pick up. Moreover, competent cells respond to environmental variations and control the rate of gene acquisition through a biological process of transformation.
• Since transformation is the most effective way of transferring DNA that has been deliberately altered into recipient cells, it is widely recognised as the preferred method of gene transfer.
• One to ten kilobases’ worth of DNA can be transferred throughout the transformation process.

Bacterial Transformation Principle

The ability of bacteria to liberate DNA that is then ingested by another competent bacterium is the basis for bacterial transformation.

• The success of transformation is contingent on the capacity of the host cell.
• Competence is the capacity of a cell to incorporate bare DNA throughout the transformation process.
• In the late stationary phase, organically transformable organisms spontaneously liberate their DNA by autolysis.
• Escherichia coli is one of the bacteria that may be manipulated in the laboratory to increase its transformability using chemicals such as calcium, a strong electric field (electroporation), or a heat shock.
• By increasing the permeability of the cell wall and allowing the donor DNA to enter, electroporation or heat shock enhance competence.
• Similarly, transformants may be selected if the transformed DNA contains a selectable marker, like antibiotic resistance, or an amino acid codifying for the utilisation of a growth factor.
• Most naturally competent bacteria attach to free DNA, which is then integrated into chromosomal DNA.
• Free DNA can sometimes be placed on plasmids which can replicate independently of the chromosome; therefore, the insert is not required to be integrated into the chromosome.
• The transformant that has undergone transformation expresses some plasmid-encoded enzymes and antibiotic-resistant markers.
• Initially, the donor DNA is inserted into the plasmid during this transformation procedure. The donor DNA-containing plasmid is then implanted into the competent host bacteria.
• Upon completion of the transformation, it is feasible to recognize the bacteria harbouring the plasmid by using growth media treated with a particular antibiotic.

Bacterial Transformation Steps

• Transformation happens in four stages:
• growth of expertise,
• DNA adherence to the cell surface
• Free DNA is processed, taken up (often in a 3′ to 5′ orientation), and then integrated into the chromosome by recombination.
• Either electroporation or thermal shock treatment may be used to create competence artificially. The choice is determined by the intended transformation efficiency, the experiment’s goals, and the available resources.
• The cell-DNA combination is exposed to a thermal shock at 0 °C and then 42 °C.
• The mixture is transferred to an electroporator, where it is treated to a brief pulse of a high-voltage electric field for electroporation.
• Double-stranded DNA that has been liberated from lysed cells interacts noncovalently with receptors on the cell surface. Since there is no identification of unique DNA sequences, these creatures may possibly integrate DNA from other species.
• Membrane-bound endonucleases pierce and fragment the bound double-stranded DNA into tiny pieces, enabling the single strand to reach the cell via a DNA translocation channel that spans the membrane.
• By recombination, the altered DNA replaces the chromosomal DNA fragment by integrating into the chromosome. However, for this integration to occur, the DNA fragment that is being donated and the DNA fragment in the chromosome must have a high degree of nucleotide sequence similarity.
• During heat shock or electroporation, the plasmid containing the donor DNA is inserted in the case of plasmid. Growing the cells in a growth medium laced with a particular antibiotic will allow you to identify the plasmid-containing cells.

Types of Bacterial Transformation

Transformation can take two different forms:

Natural Transformation

During spontaneous metamorphosis, bacteria are capable of directly ingesting DNA from their environment.

Artificial Transformation

In the event of artificial transformation, the competence of the host cell must be generated artificially by a number of techniques.

Examples of Bacterial Transformation

• As the oldest and most renowned example of bacterial transformation, the DNA of smooth-capsule-positive Streptococcus pneumonia colonies transforms into rough-capsule-negative colonies. This was the initial recognised mechanism of genetic exchange between microorganisms.
• By recognising other species, Neisseria and H. influenzae take up DNA from other species.
• In the instance of B. subtilis, natural bacterial transformation has also been noted.

References

• Verma PS and Agarwal VK (3005). Cell Biology, Genetics, Molecular Biology, Evolution and Ecology. Multicolored Edition.
• McGee, David & Coker, Christopher & Harro, Janette & Mobley, Harry. (2001). Bacterial Genetic Exchange. Doi: 10.1038/npg.els.0001416.
• Griffiths AJF, Miller JH, Suzuki DT, et al. An Introduction to Genetic Analysis. 7th edition. New York: W. H. Freeman; 2000. Bacterial transformation.Available from: https://www.ncbi.nlm.nih.gov/books/NBK21993/
• https://vlab.amrita.edu/?sub=3&brch=77&sim=1107&cnt=1

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