Transfromation Transformation was first demonstrated in 1928 by Frederick Griffith, an English bacteriologist searching for a vaccine against bacterial pneumonia. Griffith discovered that a non- virulent strain of Streptococcus pneumoniae could be transformed into a virulent one by exposure to strains of virulent S. pneumoniae that had been killed with heat.Frederick GriffithStreptococcus pneumoniae

Rough non- virulent Strain R Smooth virulent Strain S Heated Smooth Strain hS Heated hS + R Strains Mouse OK Mouse not OK Mouse OK Mouse not OK ↓↓ ↓↓ The Griffith’s bacterial infection experiment

The “Transforming principle” discovery in 1944 Oswald Avery with Colin MacLeod and Maclyn McCarty that DNA is the material of which genes and chromosomes are made.discoveryColin MacLeodMaclyn McCartyDNAgeneschromosomes

en.wikipedia.org/wiki/Frederick_Griffith 1900 picture of the Colgate band. Avery is seated in the middle holding his cornet.

Sir Henry Dale - The President of the Royal Society - on the award of the RS Copley Medal to Oswald Avery, commented: ”Here surely is a change to which, if we were dealing with higher organisms, we should accord the status of a genetic variation, and the substance inducing it – the gene, one is tempted to call it – appears to be a nucleic acid of the desoxyribose type. Whatever it be, it is something that should be capable of description in terms of structural chemistry” From Aaron Klug, “The Discovery of the DNA Double Helix”, wwwsciencedirect.com

Rough non- virulent Strain R Smooth virulent Strain S Heated Smooth Strain hS Heated hS + R Strains Mouse OK Mouse not OK Mouse OK Mouse not OK ↓↓ ↓↓

Rough non- virulent Strain R Smooth virulent Strain S Heated Smooth Strain hS Heated hS + R Strains Mouse OK Mouse not OK Mouse OK Mouse not OK ↓↓ ↓↓

Rough non- virulent Strain R Smooth virulent Strain S Heated Smooth Strain hS Heated hS + R Strains Mouse OK Mouse not OK Mouse OK Mouse not OK ↓↓ ↓↓

Transformation was first demonstrated in 1928 by Frederick Griffith, an English bacteriologist searching for a vaccine against bacterial pneumonia. Griffith discovered that a non- virulent strain of Streptococcus pneumoniae could be transformed into a virulent one by exposure to strains of virulent S. pneumoniae that had been killed with heat. In 1944 it was demonstrated that the transforming factor was genetic, when Oswald Avery, Colin MacLeod, and Maclyn McCarty showed gene transfer in S. pneumoniae. Avery, Macleod and McCarty called the uptake and incorporation of DNA by bacteria "transformation."Frederick GriffithStreptococcus pneumoniaeOswald AveryColin MacLeodMaclyn McCartygene

en.wikipedia.org/wiki/Frederick_Griffith 1900 picture of the Colgate band. Avery is seated in the middle holding his cornet.

Griffith's Experiment on Bacterial Transformation In 1928, Fred Griffith discovered a mystery that was never solved until 1944 when Avery, McCarty and MacLeod published a paper explaining the results. Here is what they did. See what conclusions you would draw. Griffith worked with a type of bacteria called pneumococcus. This bacteria causes pneumonia. The normal pneumococcus bacteria is surrounded by a slime capsule. This was called the S-strain. S-strain pneumococcus bacteria usually caused death because the slime capsule made it difficult for white blood cells to engulf and destroy the bacteria. A second strain of pneumococcus did not have this slime capsule so it was called R-strain (for rough). It did not cause an organism to die of pneumonia because the white blood cells could capture and destroy the bacteria. If you killed the bacteria by boiling it, it obviously could not reproduce and spread through the organism. So dead S-strain cells would not cause death. Here is what happened when Griffith injected various combinations of these bacteria into mice: 1. Live S-strain Inject mice with live S-strain bacteria Result: Mice died of pneumonia 2. Live R-strain Inject a mouse with live R-strain Result: Mouse lived 3. Dead S-strain Inject mice with dead S-strain bacteria Result: Mice lived 4. Mystery: Inject mice with DEAD S-stain bacteria and LIVE R-strain bacteria (neither of which should kill them). Result: Some of the mice died of pneumonia. When their blood was analyzed Griffith found LIVING S-STRAIN BACTERIA where there had been none before. These bacteria continued to reproduce as S-strain bacteria and could cause death by pneumonia. Conclusions: Where do you think the live S-cells came from? The dead S-cells came back to life. The live R-cells put on the slime capsules from the dead S-cells and avoided being destroyed by the white blood cells. The live R-cells turned into S-strain cell. The dead S-cells came back to life. The live R-cells put on the slime capsules from the dead S-cells and avoided being destroyed by the white blood cells. The live R-cells turned into S-strain cell. Click here to see how almost 20 years later, Avery, McCarty and MacLeod finally solved Griffith's mystery.

Transformation was first demonstrated in 1928 by Frederick Griffith, an English bacteriologist searching for a vaccine against bacterial pneumonia. Griffith discovered that a non- virulent strain of Streptococcus pneumoniae could be transformed into a virulent one by exposure to strains of virulent S. pneumoniae that had been killed with heat. In 1944 it was demonstrated that the transforming factor was genetic, when Oswald Avery, Colin MacLeod, and Maclyn McCarty showed gene transfer in S. pneumoniae. Avery, Macleod and McCarty called the uptake and incorporation of DNA by bacteria "transformation."Frederick GriffithStreptococcus pneumoniaeOswald AveryColin MacLeodMaclyn McCartygene

Griffith was killed at work in his laboratory in 1941, along with longtime friend and bacteriologist William M. Scott in London as a result of an air raid in the London Blitz. At the time of his death, Griffith was an obscure scientist, whose monumental discovery of pneumococcal transformation was barely known. His Lancet obituary mentions it in passing as part of a single sentence, while his obituary in the British Medical Journal does not mention it at all.[4] It wasn't until 1944 that Griffith's "transforming principle" was identified as DNA by Oswald Theodore Avery, along with coworkers Colin MacLeod and Maclyn McCarty.[5] All modern molecular biology has evolved from this work.London Blitz[4]Oswald Theodore AveryColin MacLeod Maclyn McCarty[5] Frederick Griffith was the uncle of John Stanley Griffith, a winner of the Royal Society's Faraday Medal.