Q.Describe Frederick Griffith's bacterial transformation experiment on Streptococcus pneumoniae. What result led him to conclude that a heritable 'transforming principle' had passed from the heat-killed S bacteria into the living R bacteria?
Step 1. Griffith injected mice with live S (smooth, capsule-covered, virulent) bacteria — the mice died from pneumonia.
Step 2. He injected mice with live R (rough, no capsule, non-virulent) bacteria — the mice survived.
Step 3. He injected mice with heat-killed S bacteria — the mice survived, since heat-killing destroyed the capsule protection.
Step 4. He injected mice with a MIXTURE of heat-killed S bacteria plus live R bacteria — the mice died, and live, virulent S-type bacteria were recovered from their blood.
Step 5. Since the injected S bacteria were already heat-killed and could not revive, some chemical substance from the dead S bacteria must have transferred into the living R bacteria and permanently converted (transformed) some of them into virulent S bacteria — a heritable change, since the transformed bacteria's own descendants remained virulent S-type.
Griffith concluded that a 'transforming principle' from the heat-killed S bacteria was taken up by living R bacteria and heritably transformed them into virulent S bacteria.
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