Transformation bactérienne

Bacterial transformation is the process by which bacteria take up exogenous DNA from the environment.

Some bacteria can naturally take up this exogenous DNA, while others are chemically induced in the lab to make their cell membrane permeable to DNA. This step is part of DNA cloning, which helps scientists study gene sequences, their functions, and the proteins they encode.

In the lab, the DNA sequence of interest is inserted into a circular piece of DNA called a plasmid. This DNA of interest is the exogenous DNA that will be introduced into the bacteria.

The plasmid usually also carries an antibiotic resistance gene, which helps scientists to identify bacteria that have taken up the plasmid.

A large number of copies of the plasmid are added to the liquid medium containing the competent bacteria, followed by a brief heat shock. The sudden temperature change from ice to 42°C increases membrane permeability, allowing plasmid DNA to enter the cell.

The bacteria are then grown on selective media containing a specific antibiotic, which allows only resistant cells that have taken up the cloned plasmid to survive and grow.

Only transformed cells multiply to form colonies, which are visible spots of bacterial growth derived from a single cell.