From Big Medical Encyclopedia

The FLYUKTUATSIONNY TEST — a method of definition of dependence of quantity of mutants in bacterial population from time of their emergence in the course of growth of bacterial culture.

S. E. Luria and M. Delbryuk developed F. t. in 1943 during studying of origins of the mutants of E. coli steady against a bacteriophage of T1. Essence F. is as follows: equal small amounts of bacteria of wild type bring in a medium and grow up independently from each other in identical conditions. Cultures grow of timepoint of tQ until t^. At the time of t0 select on one test from each culture and sow them on the selection environment for identification of mutant clones. In tests from those independent cultures where mutations occurred shortly before the moment of tx, or did not occur at all, mutant clones will be found in insignificant quantity or they will not be at all. If the mutation in any of independent cultures occurred long before the moment of tK, then thanks to reproduction of a mutant individual the quantity of mutant clones at the time of tx will be considerable. The quantity of the mutant clones which arose in tests from a number of independent cultures strongly varied, i.e. fluctuation was observed. In a series of tests from the same culture of distinction in number of mutant clones were insignificant.

Importance of results F. t. it is usually estimated by means of comparison of values of dispersions for the row reflecting quantity of mutant clones from independent cultures, and the corresponding row for tests from the same culture. At Poisson distribution (a kind of random distribution) dispersion is close or in number equal to the average arithmetic size of this row. If dispersion of number of mutants is one test much more value of their arithmetic-mean number, then it demonstrates uneven distribution of mutants between tests.

If the changes leading to emergence of bacteria with a mutant phenotype are a consequence of adaptation of a certain part of bacterial population to action of a selective factor (a selektiruyushchy factor), it was necessary to expect that in tests from independent cultures the quantity of clones with the changed phenotype will correspond to Poisson distribution (i.e. to submit to laws of accidental processes). However in an experiment of it did not observe. Thus, by means of F. t. the mutational, but not adaptation nature of variability of bacteria was proved that allowed to draw a conclusion

on independence of emergence of mutations (see the Mutation) from action of the agent or a selective factor.

In genetic researches F. t. widely apply to definition of a mutation rate counting on one cell for one generation.

Bibliography: Zakharov I. A. and K. V. Genetik's Receipt of microorganisms,

L., 1967; G.'s Stent and To e l and N -

d and r River. Molecular genetics, the lane with English, M., 1981; Heys U. Genetika of bacteria and bacteriophages, the lane with English, M., 1965; Luria S. E. a. D e 1-b r ii with k M. Mutations of bacteria from virus sensitivity to virus resistance, Genetics, v. 28, p. 491, 1943. G. B. Smirnov.