Question

3. A) Why is it necessary to include ampicillin in the medium with the (-) plasmid treatment? B) of the (+) plasmid treatment? the two genes of interest on the plasmid were only expressed on the plate with ampicillin. Why? 15. What causes the "halo effect", the white satellite colonies around the green fluorescent colonies, in the (+) plasmid TSA + ampicillin plate? (6. Other than transformation, what are two other mechanisms that bacteria use to acquire new genes?

Answer 1

1)Plasmid contains gene for ampicillin resistance which makes the presence of ampicillin necessary in the medium as it acts as a selection marker for transformed and untransformed cells for both +plasmid and - plasmid treatment.

Ampicillin acts by inhibiting the growth of E.Coli .Only the transformed cells can produce Ampicillin resistant gene and can survive.

2) The genes of interest on plasmid is expressed only in the presence of Ampicillin because the transformed cells can be identified by their ability to survive in an environment that contains the antibiotic ampicillin.

3) The white satellite colonies appear because some of the untransformed cells grow around the transformed cells which produce b- lactamase that inhibits Ampicillin.

They are white due to the absence of pGAL DNA gene which is codes for b-galactosidase .it is absent as they are not Ampicillin resistant.

4) Transduction and conjugation are other types of gene transfer.

Transduction - DNA is transferred by a virus ( bacterophage).

Conjugation- DNA is transferred by a tube between cells.