Dead lethal bacteria + Live nonlethal bacteria --> Death! (Griffith's experiment)

Frederick Griffith's discovery of bacterial transformation was fundamental to modern biology. Several major modern technologies depend upon this phenomenon, including transgenic organisms and molecular cloning. In 1928 he performed a series of experiments studying mice experimentally infected with two types of pneumococcal bacteria.

The "rough" (R) strain of bacteria can be recognized by the mouse's immune system, and the mouse survives infection.

The "smooth" (S) strain of bacteria cannot be recognized, and the mouse perishes.

When the S strain is killed by heat, the bacteria is inactive, and the mouse will survive infection with this heat-killed S strain.

However, when live R strain and heat-killed S strain are combined, the mouse dies.

This work was the impetus for the famous Avery-MacLeod-McCarthy and Hershey-Chase experiments.
Supplementary papers:
1) Avery-MacLeod-McCarthy
Discovery that bacteria transform with DNA, not proteins

2) Hershey-Chase
Discovery that viruses infect host cells with DNA, not proteins

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