In order for bacteria to uptake recombinant plasmids and be transformed the DNA needs to be made competent.
Bacterial cell walls have a negative charge and will uptake DNA when made competent by adding a solution of Calcium chloride and then subjecting them to heat shock so the cell wall becomes more permeable.
Plasmids are taken up by only some bacteria. A way to test which bacteria have been transformed is to insert another gene such as an antibiotic resistant gene. By inserting this gene as well you can than expose the bacteria to that particular antibiotic and those who survive are those who have taken up the antibiotic resistant gene and the gene of interest. Once the transformed bacteria have been identified they can be subjected to optimal conditions to grow and continue to reproduce the gene of interest.
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