Newcombe experiment

The Newcombe experiment is an experiment carried out by Howard B. Newcombe and published in 1949, with which it can be shown that random mutations in bacteria occur spontaneously, and not just in response to changed environmental conditions. Newcombe thus confirmed the result of the Luria-Delbrück experiment published by Salvador Edward Luria and Max Delbrück around 1943 , which also confirms the occurrence of random mutations, even in the absence of selection mechanisms .

Experiment description

In the experiment, bacteria are incubated in a Petri dish for a few hours and then transferred using the replica plate method to two further Petri dishes that have been treated with bacteriophages . While the first of the two Petri dishes is being incubated directly, the bacteria are first distributed on the second with a Drigalski spatula .

Due to random mutations, some bacterial cells are already resistant to the attached bacteriophages at this point . These individual cells can form new, resistant cell colonies after they have been distributed over the entire Petri dish . Therefore, after incubation, significantly more surviving (i.e. resistant) bacteria can be observed on the second, distributed Petri dish than on the first Petri dish.

Newcombe was thus able to demonstrate that the mutations were already present before the bacteriophages were subjected to selection pressure . The alternative hypothesis, according to which bacteria only develop resistance in response to the attack by phage, has been refuted.

literature

• Howard B. Newcombe, Roma Ha Wirko: Spontaneous mutation to streptomycin resistance and dependence in Escherichia coli . In: Journal of Bacteriology . tape 57 , no. 5 , May 1949, p. 565-572 , PMID 16561734 , PMC 385560 (free full text).