🔬 Clear-Plaque Mutant

Discussion

<p>The turbidity of plaques formed by wild-type temperate phages are a consequence of microcolony formation by lysogens that grow over the course of plaque formation, that is, microcolonies that are initiated early on during plaque formation from bacteria in which lysogenic cycles have been initiated. Phages that are unable to form lysogens thus fail to produce these phage-resistant, i.e., phage-immune microcolonies, and as a consequence remain clear (typically meaning relatively free of intact bacteria).

From the glossary of Hershey (1971), p. 773, note this definition of "clear", as in, "clear" plaque: "Lambda and other temperate phages form plaques that are turbid owing to growth of cells wikipedia.org/wiki/Survival" target="_blank" class="bap-term">surviving the infection. Mutants forming clear plaques (clear mutants) establish immunity less efficiently and permit fewer cells to survive."

From Ptashne (2004), p. 68: "Most of these clear mutants bear a lesion in one of three genes: cI, cII, or cIII. It is possible to isolate a rare lysogen of a cII or cIII mutant; once isolated the lysogen is stable, immune, and inducible by ultraviolet light. But it is never possible to isolate a lysogen of a cI mutant."

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