Question

What would happen when one grows a recombinant bacterium in a bioreactor but forgets to add an antibiotic to the medium in which the recombinant is growing?

Answer 1

Consequences of absence of antibiotic in the medium:

A plasmid vector generally has an antibiotic resistance gene in it as a selectable marker. This confers antibiotic resistance to the host cells which get transformed with the plasmid. If they lose the plasmid, they get susceptible to the antibiotics and can die. This forces the host cells to keep the plasmid in them.

If the recombinant DNA has an antibiotic resistance gene incorporated into it, then forgetting the addition of antibiotic fails to prevent the growth of host cells which have not uptaken the plasmid (non-transformants). Since, maintaining a high copy number of plasmids is a metabolic burden to the microbial cells, they will tend to lose the plasmid.

The non-transformants might outgrow the transformants resulting in less product formation and wastage of nutrients and culture media.