Q.Read the following passage below and answer next four questions (23 - 26) related to it : In his experiment Griffith isolated two strains of bacteria, one was rough walled with pili on the wall and the other one covered with an extremely slimy coat hence smooth in nature. He injected type II R to mice and the mice could survive. Type III S was injected to mice and it died of Pneumonia. Heat killed (HK) strains of the same (Type III S) when injected to the mice, it was alive or did not die. But when the mice was injected with III S (HK) and II R mixed the mice was found to be dead and virulent III S were recovered from the dead remains of the mice. [Q23] Name the process which is observed in this experiment :

In Griffith's 1928 experiment, live avirulent R bacteria mixed with heat-killed virulent S bacteria killed the mice and yielded live S bacteria. The R bacteria were genetically 'transformed' by material from the dead S cells — the process of bacterial transformation.

Griffith worked with Streptococcus (Diplococcus) pneumoniae:

• Live S (smooth, virulent) → mice die.
• Live R (rough, avirulent) → mice live.
• Heat-killed S → mice live.
• Heat-killed S + live R → mice die, and live S are recovered. …

Griffith performed his transformation experiment on the bacterium Streptococcus pneumoniae, historically called Diplococcus pneumoniae, which causes pneumonia in mammals.

The bacterium used by Frederick Griffith (1928) was Streptococcus pneumoniae (older name Diplococcus pneumoniae), the causative agent of pneumonia. It occurs as two strains: the virulent S (smooth, capsulated) type and the avirulent R (rough, non-capsulated) type. The other options — Bacillus subtilis, *Haemoph …

The type III S strain is smooth (S = smooth, capsulated); heating only kills it, it does not change its smooth wall to rough. So saying HK III S was 'rough in nature' is incorrect.

Evaluating each statement about heat-killed (HK) type III S:

• (a) "Heat killed III S strain was rough in nature" — INCORRECT. The S strain is smooth (has a mucous/polysaccharide capsule); heat kills the cells but does not convert its smooth wall into a rough one.
• (b) "Avirulent" — correct; once heat-killed, the S cells cannot cause disease.
• (c) "Heat killed III S strain was smooth in nature" — correct; it retains its smooth (capsulated) character. …

When HK III S and live II R are given together, the transforming principle (DNA) from the heat-killed S enters the living R cells and transforms them into virulent S bacteria — so the mixture becomes deadly.

Heat-killed III S alone is harmless, and live II R alone is harmless. But together, genetic material (the 'transforming principle', later identified as DNA) released from the dead S cells is taken up by the living R cells. This converts (transforms) the avirulent II R into virulent III S bacteria, which multiply, cause pneumonia, and kill the mice — and virulent S can be recovered from the dead mice.

…

In Griffith's experiment the virulent S-strain kills mice, while the non-virulent R-strain does not.