Final answer:
The term for the clearing made by bacteriophages in a bacterial lawn on an agar plate is called a plaque. These plaques form as a result of the lytic cycle of bacteriophages, where they infect, replicate within, and subsequently lyse bacteria.
Step-by-step explanation:
The clearing made by bacteriophages in a "lawn" of bacteria on an agar plate is called a plaque. These clearings, or plaques, are areas where the bacteriophages have infected and lysed the bacterial cells.
The plaques are visible as clear zones on an otherwise opaque lawn of bacteria because the bacteriophages replicate within the infected bacteria, which results in the lysis and subsequent clearing of the bacteria. This phenomenon is part of the lytic cycle, where the bacteriophage takes over the cell to produce new phages and ultimately destroys the host cell,
In the context of a laboratory setting, when a dilute solution containing phages is spread on the bacterial lawn, they infect a certain number of cells. After about a day, clear areas appear, indicating where the individual phages first infected and lysed bacterial cells. If, for example, 10 µl of a dilution spread on the bacterial lawn infects 500 E. coli cells, 500 plaques would form. Each plaque originates from a single virus and contains a clone of the same recombinant phage DNA.