Griffith's experiment
Griffith's experiment , carried out by Frederick Griffith in 1928 , was the first evidence of transformation in a bacterium, i.e. the transfer of genetic information between bacteria .
He experimented here with the bacterium pneumoniae Streptococcus , which in mice pneumonia causes. This bacterium occurs in two variants: as "S cells" ( smooth ), which can form mucous capsules and therefore appear smooth in the light microscope and are pathogenic . The "R-form" ( rough ), on the other hand, has lost the ability to form capsules, appears rough and is not pathogenic because it is recognized by the mouse's immune system because of the missing protective capsule.
The Griffith experiment now consists of the following four steps:
- Mice injected with S-form pneumococci develop pneumonia.
- Mice injected with R-form pneumococci remain healthy.
- Heat-killed S-shape pneumococci are injected. The animals do not get sick. Dead pneumococci are therefore not pathogenic.
- If mice are injected with the killed S-form together with the living R-form, they become ill and die. Living S-form bacteria can be detected in the blood of the diseased mice.
This proved that a transformation had taken place: the pathogenic ability to form mucous capsules is transferred from the dead S cells to the living R cells.
In 1944, Oswald Avery and his colleagues showed in an experiment that the transformation is based on the transfer of deoxyribonucleic acid (DNA). This was an important step towards the realization that DNA is generally the carrier of genetic information.
literature
- Griffith F: The significance of pneumococcal types . In: Journal of Hygiene . 27, No. 2, January 1928, pp. 113-59. doi : 10.1017 / S0022172400031879 . PMID 20474956 . PMC 2167760 (free full text).
- Modern Genetics - An Introduction , TA Brown, Spektrum Akademischer Verlag, 1993 (English original: Genetics: A Molecular Approach, Second edition , Chapman & Hall 1992), ISBN 978-3860251805