Question

When living R-type of bacteria were mixed with heat-killed S-type, they converted or changed to ‘S’ type. What is this phenomenon called?

Answer 1

Hint: Griffith conducted several experiments on a bacteria. He used two different strains of bacteria, the S-type and the R-type for his experiments. Griffith was able to devise his transformation principle based upon his experimental findings.

Complete step by step answer: Griffith experimented with the Streptococcus pneumonia bacteria. This bacterium is responsible for causing pneumonia. He found that this bacterium occurred in paired form. It had two strains. One is R-strain and another one is S-strain. However, the non-capsulated strain was the R-type and the capsulated strain was S-type. Also, the capsulated strain is virulent. The experiment of Griffith had four phases.
1. He injected the R-type living bacteria into the mice and the mice were alive.
2. He injected the S-type living bacteria into the mice and the mice were dead.
3. He injected the heat-killed S-type bacteria into the mice and the mice were alive.
4. He injected the R-type living bacteria and the heat-killed S-type bacteria into the mice and the mice were dead.
The mice died into the fourth phase because when the bacteria were heat-killed its DNA got fragmented in the process. When this heat-killed S-type was mixed with the R-type living bacteria then the fragmented DNA from the heat-killed S-type got diffused into the DNA of the R-type living bacteria. Due to this the R-type, living bacteria got transformed into the S-type living bacteria and became virulent. It thus infected the mice and it got killed. This phenomenon is known as Transformation. Transformation is the process of conversion of the non-capsulated bacteria into the capsulated bacteria due to the transfer of the DNA from the capsulated strain to the non-capsulated strain.

Note: Transformation is often confused with transduction. Transduction is the transfer of the genetic material from one bacterium to another through a virus that is known as the bacteriophage. It was first observed in the Salmonella bacteria, the bacteria that is responsible for causing typhoid.