F Griffith’s Experiment (i) The two strains of bacterium Streptococcus pneumoniae (causing pneumonia) one forming smooth colonies with capsule (S-type) and the other forming rough colonies without capsule (R-type) were taken for the experiment. (ii) The S-type cells were virulent and R-types were not virulent. (iii) When live S-type cells were injected into the mice, they died. (iv) When live R-type cells were injected into mice, they did not show pneumonia. S-strain —– > Injected into mice ———- >Mice died R-strain —– > Injected into mice ———- >Mice lived (v)When S-strain bacteria were killed by heating and injected into the mice, they did not develop disease. S-strain —– > (heat-killed) —– > Injected into mice—-> Mice lived (vi)When a mixture of heat-killed S-type cells and live R-cells were injected into the mice, the mice died of pneumonia. (vii)Griffith recovered living S-strain cells from the dead mice.. (viii) According to him, R-strain bacteria had somehow been transformed by the heat-killed S-strain bacteria. This may be due to some transforming principle. A factor may be transferred from the heat-killed S-strain, which enabled the R-strain to synthesise a smooth capsule and become virulent. (ix) This transforming principle must be the genetic material.
In a series of experiments with Streptococcus and mice, F Griffith concluded that R-strain bacteria had been transformed. Explain.
Answers
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F Griffith’s Experiment
(i) The two strains of bacterium Streptococcus pneumoniae (causing pneumonia) one forming smooth colonies with capsule (S-type) and the other forming rough colonies without capsule (R-type) were taken for the experiment.
(ii) The S-type cells were virulent and R-types were not virulent.
(iii) When live S-type cells were injected into the mice, they died.
(iv) When live R-type cells were injected into mice, they did not show pneumonia.
S-strain —– > Injected into mice ———- >Mice died
R-strain —– > Injected into mice ———- >Mice lived
(v)When S-strain bacteria were killed by heating and injected into the mice, they did not develop disease.
S-strain —– > (heat-killed) —– > Injected into mice—-> Mice lived
(vi)When a mixture of heat-killed S-type cells and live R-cells were injected into the mice, the mice died of pneumonia.
(vii)Griffith recovered living S-strain cells from the dead mice..
(viii) According to him, R-strain bacteria had somehow been transformed by the heat-killed S-strain bacteria. This may be due to some transforming principle. A factor may be transferred from the heat-killed S-strain, which enabled the R-strain to synthesise a smooth capsule and become virulent.
(ix) This transforming principle must be the genetic material.