Question

In a series of experiments with Streptococcus and mice F. Griffith concluded that R-strain bacteria had been transformed. Explain.

Answer 1

In this experiment, bacteria from the III-S strain were killed by heat, and their remains were added to II-R strain bacteria. While neither harmed the mice on their own, the blend of the two was able to kill mice.

Griffith was also able to get both live II-R and live III-S strains of S. pneumoniae from the blood of these dead mice. He concluded that the type II-R had been "transformed" into the lethal III-S strain by a "transforming principle" that was somehow part of the dead III-S strain bacteria.[3]

Today, we know that the "transforming principle" Griffith saw was the DNA of the III-S strain bacteria. While the bacteria had been killed, the DNA had survived the heating process and was taken up by the II-R strain bacteria. The III-S strain DNA contains the genes that form the shielding polysaccharide part from attack.