Transfromation
Transformation was first demonstrated in 1928
by Frederick Griffith, an English bacteriologist
searching for a vaccine against bacterial
pneumonia. Griffith discovered that a nonvirulent 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.
The Griffith’s bacterial infection experiment
Rough nonvirulent
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 “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.
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 nonvirulent
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 nonvirulent
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 nonvirulent
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 nonvirulent 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."
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.
Transformation was first demonstrated in 1928
by Frederick Griffith, an English bacteriologist
searching for a vaccine against bacterial
pneumonia. Griffith discovered that a nonvirulent 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."
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.
Frederick Griffith was the uncle of John Stanley Griffith, a
winner of the Royal Society's Faraday Medal.