Selective media helps researchers identify their desired mutant host cell colonies during gene cloning. Specifically, these media tell you which recipient host cells took up the vector versus those that did not during the steps of horizontal gene transfer.

Article table of contents:

Antibiotic-based selection media

Phenotypic lag

Distinguishing between recombinant and non-recombinant vectors

Drop-out media for selection

Experimental considerations for choosing antibiotic versus drop-out media for selection of transformants


Antibiotic-based selection media

Antibiotic-based selection uses an antibiotic added to media to screen desired transformed cells. Transformed cells will have a selectable marker gene on the plasmid within that provides antibiotic resistance, allowing these cells to grow on selective media while untransformed cells will not.

Here is an illustration of this type antibiotic selection using a simple transformation experiment.

Illustration of antibiotic-based selection of host cells during gene cloning procedure

Figure 1. Represents antibiotic-based selection of host cells during gene cloning procedure.

In figure 1, the recipient host cells are transformed with a plasmid (or any other suitable vector) that has a gene cassette conferring resistance to antibiotic 'A,’ as we’ll call it for simplicity.

When plated on media containing antibiotic A, only the cells that have taken up the vector grow and produce colonies.

Cells that have not taken up the plasmid - the non-transformed cells will be killed by antibiotic A and do not produce colonies on this selective medium.

Some cells will take up the vector, and some won’t. You want the former in order to move forward with the next steps in your cloning procedure. And antibiotic-based selection eliminates cells that did not take up the vector, making the process of identifying your successfully transformed cells easy.

Common selective antibiotics used in cloning experiments include Carbenicillin, Gentamicin, Tetracycline, Kanamycin, Ampicillin etc.