Griffith's Experiment
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Griffith's experiment
Griffith's experiment discovering the "transforming principle" in pneumococcus bacteria.
Griffith's experiment, reported in 1928 by Frederick Griffith,[1] was one of the first experiments suggesting that bacteria are capable of transferring genetic information through a process known as transformation.[2][3]
Griffith used two strains of pneumococcus (Streptococcus pneumoniae) bacteria which infect 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. A German bacteriologist, Fred Neufeld, had discovered the three pneumococcal types (Types I, II, and III) and discovered the Quellung reaction to identify them in vitro.[4] Until Griffith's experiment, bacteriologists believed that the types were fixed and unchangeable, from one generation to another.
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 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 of 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 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 protective polysaccharide capsule. Equipped with this gene, the former II-R strain bacteria were now protected from
Griffith's experiment
Griffith's experiment discovering the "transforming principle" in pneumococcus bacteria.
Griffith's experiment, reported in 1928 by Frederick Griffith,[1] was one of the first experiments suggesting that bacteria are capable of transferring genetic information through a process known as transformation.[2][3]
Griffith used two strains of pneumococcus (Streptococcus pneumoniae) bacteria which infect 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. A German bacteriologist, Fred Neufeld, had discovered the three pneumococcal types (Types I, II, and III) and discovered the Quellung reaction to identify them in vitro.[4] Until Griffith's experiment, bacteriologists believed that the types were fixed and unchangeable, from one generation to another.
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 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 of 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 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 protective polysaccharide capsule. Equipped with this gene, the former II-R strain bacteria were now protected from