Griffiths Transformation Experiment

•  Frederick Griffith in 1928 when he demonstrated that a physical trait can be passed from one cell to another.
• He was working with two strains of the bacterium Streptococcus pneumoniae identified as S and R. When a bacterial cell is grown on solid medium, it undergoes repeated cell divisions to form a visible clump of cells called a colony.
• The S type of S. pneumoniae synthesizes a gelatinous capsule composed of complex carbohydrate (polysaccharide). The enveloping capsule makes each colony large and gives it a glistening or smooth (S) appearance. This capsule also enables the bacterium to cause pneumonia by protecting it from the defense mechanisms of an infected animal.
• The R strains of S. pneumoniae are unable to synthesize the capsular polysaccharide; they form small colonies that have a rough (R) surface  This strain of the bacterium does not cause pneumonia, because without the capsule the bacteria are inactivated by the immune system of the host.
• Mice injected with living S cells get pneumonia.
•  Mice injected either with living R cells or with heat killed S cells remain healthy.
• Mice injected with a mixture of living R cells and heat-killed S cells contract the disease and often die of pneumonia .
• Bacteria isolated from blood samples of these dead mice produce S cultures with a capsule typical of the injected S cells, even though the injected S cells had been killed by heat.
•  Evidently, the injected material from the dead S cells includes a substance that can be transferred to living R cells and confer the ability to resist the immunological system of the mouse and cause pneumonia.
• In other words, the R bacteria can be changed or undergo transformatio into S bacteria. 
•