Hayes, W. (1966). Genetic Transformation: a Retrospective Appreciation First Griffith Memorial Lecture. Journal of General Microbiology, 45(3), 385-397. doi:10.1099/00221287-45-3-385

Research question:  The original purpose of Griffith’s experiment was to test whether or not the bacteria synthesized their own polysaccharide capsule. He eventually answered how non-capsulated strains of Pneumococcus bacteria became virulent by providing them with capsular material from another strain. 

 

Griffith discovered his transformation in 1928 in England. He observed that mice given injections of the nonvirulent strain died and had virulent capsulated bacteria. Griffith hypothesized that the nonvirulent bacteria did not lose its ability to to synthesize capsular polysaccharide hence when they were injected, a sufficient concentration of polysaccharide might have been present to enabling the formation of a normal capsular synthesis. His goal was to determine that non-capsulated strains can be made virulent by providing them with capsular material from another strain. In the experiment, Griffith studied two strains of bacteria from Pneumococcus bacteria, type III-S and type II-R. He used mice as his experimental subjects. He obtained a mixture of small numbers of living non-virulent bacteria and suspensions of heat killed virulent organisms, both which did not form virulent bacteria when injected alone. The first step of his experiment was injecting the mice with both the S and R strain. The mice with S strain died while the mice with R strain lived. The S bacteria formed a smooth polysaccharide capsule allowing it to protect itself from the mouse immune system. For the mice injected with the R strain, the mice survived. R bacteria lacked the smooth polysaccharide making it nonvirulent. The next step in his experiment was injecting the mice with S strain that had been killed by heat. All the mice lived indicating that the bacterial strain was ineffective. When he injected mixtures of the of the living avirulent bacteria and the heat-killed suspensions, mice died from septicaemia and capsulated virulent organisms was found in their blood. This reflected that the dead S strain entered information into the live R strain. When harmless R strain was injected into the mice and the heat killed bacteria in S strain, the dead mice contained the living S bacteria. Overall, he discovered the R strain bacteria had taken up “transformed material” from the heat killed S strain. He called this phenomenon transformation.

 

Noorulain Paracha