Griffith's experiment
Grif ? th 's e xp erim en t d is c o ve rin g t h e " t ra n sfo rm in g
p rin cip le " in p neu m oco ccu s b acte ria .
Grif?th's experiment , r epor ted in 1928 b y
Frederick Grif?th ,
1
was the ?rst
experiment suggesting that bacteria ar e
capable of transferring genetic information
through a pr ocess known as
transformation .
2 3
Grif?th 's ?ndings wer e
followed by resear ch in the late 1930s and
early 40s that isolated DNA as the material
that communicated this genetic
information.
Pneumonia was a serious cause of death
in the wak e of the post-WWI Spanish
influenza pandemic , and Grif?th was
studying the possibility of cr eating a
vaccine. Grif?th used two str ains of
pneumococcus ( Strept ococcus
pneumoniae ) bacteria which inf ect mice –
a type III-S (smooth) which was virulent,
and a type II-R (rough) strain which was
nonvirulent. The III-S str ain synthesized a
polysaccharide capsule that pr otected
itself from the host' s immune system ,
resulting in the death of the host, while the
II-R str ain did not ha ve that pr otective
capsule and was def eated by the host' s
immune system. A German bacteriologist,
Fred Neuf eld , had disco ver ed the thr ee
pneumococcal types (T ypes I, II, and III)
and discover ed the Quellung r eaction to
identify them in vitr o.
4
Until Grif?th's
experiment, bacteriologists belie ved that
the types were ?xed and unchangeable,
from one gener ation to another .
In this experiment, bacteria from the III-S
str ain wer e killed b y heat, and their
remains wer e added to II-R strain bacteria.
While neither alone harmed the mice, the
combination was able t o kill its host.
Grif?th was also able to isolate both live II-
R and live III-S str ains of pneumococcus
from the blood of these dead mice. Grif?th
concluded that the type II-R had been
"tr ansformed" int o the lethal III-S str ain by
a "transforming principle " that was
somehow part of the dead III-S str ain
bacteria.
Toda y, we know that the "tr ansforming
principle" Grif?th obser ved was the DN A of
the III-s str ain bacteria. While the bacteria
had been killed, the DN A had survived the
heating pr ocess and was tak en up by the
II-R strain bacteria. The III-S str ain DNA
contains the genes that form the smooth
protectiv e polysaccharide capsule.
Equipped with this gene, the former II-R
str ain bacteria wer e now protected fr om
the host's immune system and could kill
the host. The exact natur e of the
transforming principle (DN A) was veri?ed
in the experiments done b y Aver y, McLeod
and McCar ty and by Hershe y and Chase .
1 . Grif?th, Fred. (Januar y 1928). "The
Signi?cance of Pneumococcal T ypes" .
Journal of Hygiene . Cambridge Univ ersity
Press. 27 (2): 113–159.
doi :10.1017/S0022172400031879 .
JST OR 4626734 . PMC 2167760 ? .
PMID 20474956 .
2 . Lorenz, M. G.; W ackernagel, W . (1994-09-
01). "Bacterial gene tr ansfer by natur al
genetic tr ansformation in the
environment" . Microbiological Re views . 58
(3): 563–602. PMC 372978 ? .
PMID 7968924 .
Notes
3 . Downie, A. W. (1972). "Pneumococcal
transformation — a backwar d view: Fourth
Grif?th Memorial Lectur e" (P D F) . Journal of
Gener al Micr obiology . 73 (1): 1–11.
doi :10.1099/00221287-73-1-1 .
PMID 4143929 . Retrie ved 2011-11-30 .
4 . Lehr er, Ste ven. Explor ers of the Body .
2nd edition 2006 p 44
Aver y, MacLeod, and McCar ty (1944).
"Studies on the Chemical Natur e of the
Substance Inducing Transformation of
Pneumococcal T ypes: Induction of
Transformation b y a Desoxyribonucleic
Acid Fraction Isolated fr om
References
Pneumococcus Type III" . Journal of
Experimental Medicine . 79 (1): 137–158.
doi :10.1084/jem.79.2.137 .
PMC 2135445 ? . PMID 19871359 .
(References the original experiment
by Grif?th. Original ar ticle and 35th
anniversary reprint available. )
Daniel Har tl; Elizabeth Jones (2005).
Genetics: Analysis of Genes and
Genomes, 6th edition . Jones & Bar tlett.
854 pages. ISBN 0-7637-1511-5 .
Lehrer, Ste ven (2006). Explor ers of the
Body (2nd ed.). United States: iUniv erse,
Inc. ISBN 0-595-40731-5 .
Further reading
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