Lakhasly

In 1952, Zinder and Lederberg performed a series of experiments on the typhoid bacterium Salmonella typhimurium; the results of which elucidated the phenomenon of transduction.When this fluid was mixed with met-thr+ cells prototrophic cells for methionine and threonine were produced.

In 1952, Zinder and Lederberg performed a series of experiments on the typhoid bacterium Salmonella typhimurium; the results of which elucidated the phenomenon of transduction. They used two strains of Salmonella; one is prototrophic for the amino acid methionine and auxotrophic for the amino acid thrionine that may be labeled meth+thr- and the other is prototrophic for the amino acid threonine and auxotrophic for the amino acid methionine and may be labeled met-thr+. Zender and Lederberg found that when cultures of the two strains are mixed and re-cultured on a medium lacking the two amino acids, a prototrophic strain is produced. In another experiment, they used met+thr- strain that was infected by the lysogenic virus P22, and centrifuged the culture to throw down the living cells, and the supernatant fluid was heated. When this fluid was mixed with met-thr+ cells prototrophic cells for methionine and threonine were produced. From these results, Zinder and Lederberg suspected that a gene for prototrophy is transferred in the supernatant with the viral DNA. The P22 phage is a lysogenic phage that integrates its DNA, as a prophage, in the bacterial genome and remains in this temperate state