Fred Griffith
1877-1941
English bacteriologist whose studies of pneumococci, the bacteria that cause pneumonia, suggested that bacteria could undergo some kind of genetic transformation. The virulence of pneumococci depends on the presence of a polysaccharide capsule.
Virulent strains with a polysaccharide coat were known as type S; bacteria without the capsule were type R. When mice were inoculated with a mixture of living R and heat-killed S bacteria, they became infected. Griffith was able to isolate living S bacteria from these animals. Later researchers proved that the transforming factor was DNA.
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