Question

1. Two curious scientists, Gregor and Barbara, were studying E.coli infected with a virulent bacteriophage. They noticed that most of the bacteria were lysed, but a few survived. Gregor hypothesized that the bacteriophage induced the resistance in the cells, while Barbara hypothesized that the resistant mutants probably already existed. To test this, they seeded E. coli onto a petri dish which grew 10⁵ colonies, and replica plated this master plate. They pipette a suspension of the bacteriophage onto each of the three replica plates. What should they see if Gregor is correct? What should they see if Barbara is correct?

Answer 1

Gregor proposed the mutations are generated in response to the bacteriophage, 105 colonies were grown on the plate, when these colonies are replica plated to three different plates containing bacteriophage, different colonies will survive, in those plates, that is the position of live colonies will be different in different plates, only those bacterias where mutations are induced can grow, and the size of the colonies will be small because all cells in the colonies cannot get mutation.

Barbara proposed mutations were already present in the bacteria, 105 colonies were grown on the plate, when these colonies are replica plated to three different plates containing bacteriophage, same colonies will survive on those plates, that is the position of the live colonies in the three plates will be same, this is because mutations were already present and those colonies which are resistant to the phage, will survive on all three plates.