Joshua and Esther Lederberg devised a simple technique, called the replica plati
ID: 81825 • Letter: J
Question
Joshua and Esther Lederberg devised a simple technique, called the replica plating method, to test colonies of microorganisms under different growth conditions. A master plate, containing the colonies to be tested, is pressed onto a sterile velvet surface, depositing some cells from each colony in the same pattern as on the master plate. Then fresh culture plates are pressed onto the velvet to pick up cells in the same pattern. The transferred cells can be grown on different media or at different temperatures than the original colonies. Suppose the plates below represent a master plate and replicate plates. Which of the colonies (circled numbers) would you conclude have growth mutations? What kinds of mutations do you suspect? Explain your reasoning.Explanation / Answer
Answer:
1. Replica plate (SD plate at 30 degree C) does not allow growth of colonies 3 and 4 as compared to the master plate. This suggests that colonies 3 and 4 have mutations which does not allow them to grow under acidic conditions (i.e, they are not dermatophytes).
Sabouraud Dextrose Agar (SDA) is a selective medium primarily used for the isolation of dermatophytes, other fungi and yeasts but can also grow filamentous bacteria such as Nocardia. The acidic pH of this medium (pH about 5.0) inhibits the growth of bacteria but permits the growth of yeasts and most filamentous fungi.
2. Replica plate (YPD plate at 37 degree C) does not allow growth of colonies 6 and 8 as compared to the master plate. This suggests that colonies 6 and 8 have mutations which does not allow them to grow at 37 degree C. So, these are temperature sensitive mutants.
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