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"In transformation the living cell picks up fragments of DNA that have been released by dead cells. Thus, the living cell gets additional DNA." Bacterial transformation was discovered by Griffith in 1928, who used two strains of the bacterium Diplococcus pneumoniae. In the wild type strains (smooth) the cells have a carbohydrate capsule and are virulent (pathogenic). If injected into mice the smooth strain causes severe septicemia and death. A mutant strain (rough) without capsules is avirulent (non pathogenic). Heat killed smooth cells are avirulent. Griffith found that when the non capsulated variety was injected into a mouse along with heat killed encapsulated variety; a small fraction of the former acquired the ability to produce a capsule and became virulent. Griffith thought that the transforming agent was a protein.
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