Abstract
A halo plaque assay has been developed for the detection of nondefective lambda transducing phage carrying functional alleles of the metB gene of Escherichia coli K12. The assay is based upon the production of phage plaques on lawns of metB- bacterial cells which are supplemented with limiting amounts of methionine and upon the subsequent transduction of methionine-starved cells in the lawn surrounding the plaques. The resulting prototrophic transductants give rise to a halo of bacterial growth surrounding the plaque. A precise genotype can be ascribed to the characteristic morphologies of selected haloes. This technique has general application for all biosynthetic markers.
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