Describe the various steps of Griffith’s Experiment that led to the conclusion of the Transforming Principle.

S.F. Griffith demonstrated bacterial transformation experimentally by performing experiments on Diplococcus pneumonia. It has two distinct forms – one form secretes a polysaccharide capsule which gives the colonies a smooth appearance and another form is non-capsulated which gives the colonies a rough appearance. The capsule of the smooth form is virulent and gives an infected animal, the disease pneumonia; the rough form (R) is not virulent.

The main steps are as follows:

  • Griffith conducted his experiments on Diplococcus pneumonia that causes pneumonia in mice. He injected ‘S’ type living bacteria into mice and they died due to pneumonia.
  • He then injected live non-virulent bacteria (R) into mice and they did not suffer from pneumonia.
  • He then injected heat killed virulent ‘S’ type bacteria into mice and they survived equally well.
  • In the last, he injected a mixture of heat killed ‘S’ and live ‘R’ simultaneously, the mice died with the symptoms of pneumonia. Living S type bacteria were recovered from their bodies.

This happened because of something from the dead bacteria had entered the live ones and made them virulent. This means ‘R’ type of bacteria have been transformed to‘s’ type and this process is called transformation. Thus, transformation is the transferring of characters from one strain to another using DNA extract of the former.

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