Griffith's experiment
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Griffith's experiment, conducted in 1928 by Frederick Griffith, was one of the first experiments suggesting that bacteria are capable of transferring genetic information though a process known as transformation.
Griffith used two strains of Pneumococcus (which infects mice), a type III-S (smooth) and type II-R (rough) strain. The III-S strain covers itself with a polysaccharide capsule that protects it from the host's immune system, resulting in the death of the host, while the II-R strain doesn't have that protective capsule and is defeated by the host's immune system.
In his experiment, bacteria from the III-S strain were killed by heat, and their remains were added to II-R strain bacteria. While neither alone harmed the mice, the combination was able to kill its host. Griffith was also able to isolate both live II-R and live III-S strains pneumococcus from the blood of these dead mice. Griffith 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.
Today, we know that the "transforming principle" Griffith observed was the DNA of the S strain bacteria. While the bacteria had been killed, the DNA had survived the heating process and was taken up by the R strain bacteria. The S strain DNA contains the genes that form the protective polysaccharide capsule. Equipped with this gene, the former R strain bacteria were now protected from the host's immune system and could kill it.
See also: Genetics, Hershey-Chase experiment, Oswald Theodore Avery
[edit] References
- Avery, MacLeod, and McCarty (1944). "Studies on the Chemical Nature of the Substance Inducing Transformation of Pneumococcal Types: Induction of Transformation by a Desoxyribonucleic Acid Fraction Isolated from Pneumococcus Type III". Journal of Experimental Medicine 79 (1): 137-58.
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- (References the original experiment by Griffith. Original article and 35th anniversary reprint available.)
- Daniel Hartl and Elizabeth Jones (2005). Genetics: Analysis of Genes and Genomes, 6th edition. Jones & Bartlett. 854 pages. ISBN 0-7637-1511-5.
