Question

In the plaque assay, exactly what makes up a single plaque?

Short answer

Answer: A single plaque in the plaque assay consists of lysed bacterial cells, phage particles, and potentially some remaining bacterial cells, representing the area where phage particles have infected, replicated within, and lysed the bacteria.

Step-by-step solution

Introduction to Bacteriophages

Bacteriophages, or phages, are viruses that specifically infect bacteria. They are made up of genetic material (DNA or RNA) surrounded by a protein coat. When a phage interacts with a susceptible bacterial cell, it injects its genetic material into the cell, hijacking the cell's machinery to produce more phage particles. Eventually, the cell bursts, releasing the new phage particles to infect other bacterial cells.

Plaque Assay Procedure

A plaque assay is a laboratory method used to measure the concentration of phage particles in a sample. The main steps include: 1. Dilution: Phage particles are mixed with a suspension of bacteria and diluted to obtain a range of concentrations. 2. Incubation: The phage-bacterium mixture is added to a solid culture medium (agar) and incubated for a period of time to allow phages to infect and lyse bacterial cells. 3. Observation: After incubation, the agar plate is examined for the presence of clear zones or "plaques," each of which represents the area where phage particles have infected and lysed bacterial cells.

Formation of a Single Plaque

A single plaque forms when a phage particle infects a bacterial cell within the solid culture medium. As the phage replicates within the cell, it produces new phage particles, which then infect surrounding bacterial cells. This process continues, creating a radial pattern of lysis from the initial point of infection. The bacterial cells within the plaque are destroyed, leaving a clear zone on the otherwise opaque lawn of bacteria.

Components of a Single Plaque

A single plaque is made up of several components: 1. Lysed bacterial cells: The primary component of a plaque is the area where bacterial cells have been destroyed by phage infection and lysis. 2. Phage particles: Throughout the plaque, there are numerous phage particles that have been released from lysed cells and are available to infect other bacteria. 3. Remaining bacterial cells: Along the edge of the plaque, there may be surviving bacterial cells that exhibit resistance to the phage or have not yet been infected. In summary, a single plaque in the plaque assay consists of lysed bacterial cells, phage particles, and potentially some remaining bacterial cells, representing the area where phage particles have infected, replicated within, and lysed the bacteria.