Final answer:
The answer is False. A plaque assay measures virus presence in bacterial infections, not the number of bacterial auxotrophs. Replica plating, not plaque assay, is the correct technique for detecting auxotrophs.
Step-by-step explanation:
The question is asking whether a plaque assay is used to detect the number of bacterial auxotrophs on a plate, and the answer is False. A plaque assay is actually used to measure the number of viruses that infect bacteria, not auxotrophs. The clear areas, or plaques, on the plate signify where the viruses have lysed the bacteria.
In contrast, techniques such as replica plating are used to identify bacterial auxotrophs. In replica plating, bacteria are first grown on a nutritionally complete medium and then transferred to a medium that lacks specific nutrients to determine if any of the cells are inability to grow due to a nutritional requirement imposed by a mutation, hence identifying auxotrophs.
Cells are plated on a nutritionally complete plate in addition to nutrient-deficient plates when looking for a mutant because it ensures that the cells are being transferred correctly between the plates, and the fact that the bacteria do not grow on the nutrient-deficient plates confirms their auxotrophic nature rather than simply reflecting a failure in transfer.