Screening for Lysogenic Mutant Phages Using Plaque Morphology

Take two agar plates: one containing plaques from wild-type temperate phages and one that may contain plaques from mutant temperate phages.

The wild-type phages carry regulatory genes that allow a switch between the lytic and lysogenic cycles.

The mutants with deletions in these genes primarily enter the lytic cycle.

Add a buffer and incubate with shaking to release the phage particles.

Transfer the liquid from each plate to separate tubes, centrifuge them, and collect the supernatants containing the phages.

Mix each supernatant with host bacteria, add soft agar, and pour onto an agar plate.

Incubate to form a bacterial lawn.

Wild-type phages that enter the lytic cycle lyse the host cell, producing clear plaques, while those that enter lysogeny integrate the phage genome and allow host survival, producing turbid plaques.

The mutants enter the lytic cycle, lyse infected cells, and form clear plaques, confirming the loss of lysogeny control.

The presence of only clear plaques on the plate, compared to both clear and turbid plaques on the wild-type phage plate, confirms the presence of mutant phages.