Luria-Delbrück experiment

Luria-Delbrück experiment

Luria-Delbrück experiment (1943) (also called the Fluctuation Test) demonstrates that in bacteria, genetic mutations arise in the absence of selection, rather than being a response to selection. Therefore, Darwin's theory of natural selection acting on random mutations applies to bacteria as well as to more complex organisms. Max Delbrück and Salvador Luria won the 1969 Nobel Prize in Physiology or Medicine in part for this work.

In their experiment, Luria and Delbrück inoculated a small number of bacteria into separate culture tubes. After a period of growth, they plated equal volumes of these separate cultures onto phage (virus) containing agar. If virus resistance in bacteria were caused by a spontaneous activation in bacteria--i.e., if resistance were not due to heritable genetic components, then each plate should contain roughly the same number of resistant colonies. This, however was not what Delbrück and Luria found. Instead, the number of resistant colonies on each plate varied drastically.

Luria and Delbrück proposed that these results could be explained by the occurrence of a constant rate of random mutations in each generation of bacteria growing in the initial culture tubes. Delbrück developed a sophisticated mathematical model based on this hypothesis that was entirely consistent with these results. The conclusion was that mutations in bacteria, as in other organisms, are random rather than directed. [Luria, SE, Delbrück, M. " [http://www.genetics.org/cgi/reprint/28/6/491 Mutations of Bacteria from Virus Sensitivity to Virus Resistance] ", Genetics 28:491-511 (1943).]

The results of Luria and Delbrück were confirmed in more graphical, but less quantitative, way by Newcombe. Newcombe incubated bacteria in a Petri dish for a few hours, then replica plated it onto two new Petri dishes treated with phage. The first plate was left unspread, and the second plate was then respread, that is, bacterial cells were moved around allowing single cells in some colony to form their own new colonies. If colonies contained resistant bacterial cells before entering into contact with the phage virus, one would expect that some of these cells would form new resistant colonies on the respread dish and so to find a higher number of surviving bacteria there. When both plates were incubated for growth, there were actually as much as 50 times greater number of bacterial colonies on the respread dish. This showed that bacterial mutations to virus resistance had randomly occurred during the first incubation. Once again, the mutations occurred before selection was applied. [Newcombe, H.B. "Origin of Bacterial Variants." Nature 164:150-151 (1949).]

More recently, the results of Luria and Delbrück were questioned by Cairns and others, who studied mutations in sugar metabolism as a form of environmental stress. [Cairns, J. Overbaugh, J. & Miller, S., " [http://www.nature.com/nature/journal/v335/n6186/abs/335142a0.html The Origin of Mutants] ", Nature 335: 142-145 (1988).] However, eventually this result was found to have been caused by selection for gene amplification and/or a higher mutation rate in cells unable to divide. Nevertheless, there is no evidence yet for directed mutagenesis: only those mutations that allow the cells to respond to the environmental stress accumulate in a growing population. [Slechta ES, Liu J, Andersson DI, Roth JR. " [http://www.genetics.org/cgi/content/full/161/3/945 Evidence that selected amplification of a bacterial lac frameshift allele stimulates Lac(+) reversion (adaptive mutation) with or without general hypermutability] ", Genetics, 2002 Jul;161(3):945-56]

References

External links

* [http://virtuallaboratory.net/Biofundamentals/labs/OnMutation/OnMutation.html On Mutation lab]


Wikimedia Foundation. 2010.

Игры ⚽ Поможем сделать НИР

Look at other dictionaries:

  • Luria–Delbrück experiment — The two possibilities tested by the Luria–Delbrück experiment. (A) If mutations are induced by the media, roughly the same number of mutants are expected to appear on each plate. (B) If mutations arise spontaneously during cell divisions prior to …   Wikipedia

  • Luria-Delbrück-Experiment — Das Luria Delbrück Experiment (auch Fluktuationstest) ist ein von Salvador Edward Luria und Max Delbrück erdachtes und durchgeführtes Experiment, das 1943 publiziert wurde und das ein Teil der Arbeiten war, für die Luria und Delbrück 1969… …   Deutsch Wikipedia

  • Luria — is a surname, and may refer to:* Alexander Luria, Russian neuropsychologist * Isaac Luria, a Jewish mystic in Safed * Roger de Luria, Italian Admiral * Salvador Luria, Italian microbiologist * Rabbi Solomon Luria, an Ashkenazic posek and teacher… …   Wikipedia

  • Luria — ist der Name von Alexander Romanowitsch Lurija (1902 1977), russischer Psychologe Rabbi David Luria (1798 1855), osteuropäischer Talmudgelehrter Isaak Luria (1534 1572), Kabbalist Salvador Edward Luria (1912 1991), US amerikanischer Mikrobiologe… …   Deutsch Wikipedia

  • Salvador Luria — Infobox Scientist name = Salvador Edward Luria image width = caption = birth date = August 13, 1912 birth place = Turin, Italy death date = February 6, 1991 aged 78 death place = Lexington, Massachusetts nationality = Italy, United States field …   Wikipedia

  • Max Delbrück — Not to be confused with his uncle, Max Delbrück (1850 1919), an agricultural chemist. Max Delbrück Delbrück in the early 1940s …   Wikipedia

  • Max Delbrück (Biophysiker) — Max Delbrück Max Delbrück (* 4. September 1906 in Berlin; † 9. März 1981 in Pasadena, Kalifornien) war ein deutscher, ab 1945 US amerikanischer Genetiker, Biophysiker und Nobelpreisträger …   Deutsch Wikipedia

  • Salvador Edward Luria — Salvador Luria (1969) Salvador Edward Luria (* 13. August 1912 in Turin; † 6. Februar 1991 in Lexington, Massachusetts) war ein US amerikanischer Mikrobiologe italienischer Abstammung. Luria stammte aus einer sephardisch jüdischen Famil …   Deutsch Wikipedia

  • Salvador E. Luria — Salvador Edward Luria (* 13. August 1912 in Turin; † 6. Februar 1991 in Lexington, Massachusetts) war ein US amerikanischer Mikrobiologe italienischer Abstammung. Luria entwickelt 1943 den ersten Test, um Mutationen in Bakterien zu quantifizieren …   Deutsch Wikipedia

  • Salvador Luria — Salvador Edward Luria (* 13. August 1912 in Turin; † 6. Februar 1991 in Lexington, Massachusetts) war ein US amerikanischer Mikrobiologe italienischer Abstammung. Luria entwickelt 1943 den ersten Test, um Mutationen in Bakterien zu quantifizieren …   Deutsch Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”