The Concept of Stability and Some of Its Implications

Parr, Leland W.; Robbins, Mary Louise

doi:10.1128/jb.43.6.661-684.1942

Cited by 8 publications

(3 citation statements)

References 16 publications

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“…Students of bacterial mutability are familiar with the fact that, if a mutant occurs, it always makes its appearance with a delay of at least 3, and sometimes more than 9, days after inoculation (Parr and Robbins, 1941). It has been shown (Lewis, 1934;Yudkin, 1938;Parr and Robbins, 1941) that one reason for this delay is simply the fact that a certain time must elapse before the medium will be changed so as to become "preferential" for the eventual mutlant. It is obvious that a mutant, occurring at a rate of one per million (and this is the order of magnitude of the frequency of a given bacterial mutation), would never have a chance to "show up" if the medium did not somehow favor its divisions more than the divisions of the million surrounding mother type of cells.…”

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Studies on Bacterial Mutability: The Time of Appearance of the Mutant in Escherichia coli

Zamenhof¹

1946

Journal of Bacteriology

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“…As has been stressed by Parr and Robbins (1941), "one of tl e,Puz.l f,' tors about the citrate mutant IAnd about the slow-lactose-fermenting WITHs is J. '.the delay in appearance of the mutant after the inoculation of suitable inateriaI has been made."…”

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Studies on Bacterial Mutability: The Time of Appearance of the Mutant in Escherichia coli

Zamenhof¹

1946

Journal of Bacteriology

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“…They state that not all the smears gave rise to "mutants," indicating that the number of cells capable of such modification is rather limited. Parr and Robbins (1942) made further studies of changes in coliform bacteria which occur not only under optimal conditions of cultivation, but also in the absence of special physico-chemical stimulations.…”

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Induced Autotrophism in Yeast

Leonian

Lilly

1943

J Bacteriol

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The growth ofISaccharomyces cerevisiae in vitamin-deficient media may be influenced by the quantity of the inoculum and by the length of the incubation period. Some investigators have assumed that large amounts of inoculum carry over enough vitamins to induce some growth, but the writers (1942a) have shown that the actual quantity of vitamins present in large doses of inoculum is too small to be effective. As concerns the effect of a prolonged-incubation period, some workers have postulated that it enables the yeast to bring about a slow synthesis of the missing vitamin. However, doubt is cast on the validity of this theory by the fact that when cultured on a vitamin-deficient medium and under identical conditions, the same yeast sometimes makes a considerable growth without any prolonged incubation, while at other times it does not grow; or one culture may grow well, whereas other cultures of the same series may not. When such behaviors are observed repeatedly despite rigidly controlled conditions, one is forced to conclude that this phenomenon is the expression of certain inherent qualities which remain dormant when nutritional conditions are favorable, but emerge under the stimulus of critical food situations. Using this as a working hypothesis the writers proceeded to intensify the autotrophic tendencies of various yeasts. The technic employed consisted of increasing the quantity of inoculum from 0.035 to 0.7 mg., of prolonging the incubation period from 3 to 10 days, and of successively subculturing the yeasts on media from which one of the vitamins was omitted. As the autotrophic tendencies became more pronounced with each passage, a gradual reduction was brought about in the length of the incubation time, in the quantity of the inoculum, and in the number of successive transfers until an inoculum of 0.035 mg. produced an optimum yield within 72 hours. All stock cultures were carried on a medium of the same composition as that used in the successive transfers; for instance, since yeast 1-1 was developed in the absence of thiamin, it was always carried in a solution from which thiamin was omitted. This served to check or to reduce reversions.A specific strain of yeast seems to be a composite of a great many strains. For instance, when different transfers from the same stock culture were made on a medium from which one of the essential vitamins was omitted, not all of the resulting cultures behaved the same, and rarely were they identical in all respects; thus, standardized methods failed to produce standardized or even predictable results. Some single-colony isolations made by the writers will illustrate this phenomenon. The original strain of "Gebriider Mayer" yeast

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