Question

You insert a gene for tetracycline resistance into one plasmid and a gene for ampicillin resistance into another plasmid. You successfully introduce both plasmids into a sample of E. coli cells, but fail to grow any of them in culture medium with both antibiotics present in it. What could best explain the problem?
A. Random mutation has inactivated the antibiotic resistance genes

B. Plasmid incompatibility will not allow both plasmids to persist

C. E. coli cannot maintain two plasmids

D. The plasmid(s) have integrated into the bacterial chromosome

E. A phage has neutralized one of the plasmids

F. None of the above is correct

Answer 1

Answer:

B. Plasmid incompatibility will not allow both plasmids to persist

Explanation:

The two possibilities of why the plasmids are incompatible are:

1) Both plasmids contain the same origin of replicon and compete for the same Rep proteins.

2) Tetracycline: inhibits protein synthesis by binding and inhibiting ribosomal proteins, thus ampicillin target proteins may also be inhibited.

Ampicillin: Causes cell lysis which may lead to inactivation of tetracycline activity since tetracycline needs to diffuse through membrane porin channels prior binding and inhibiting ribosomal proteins.