Induced Autotrophism in Yeast

Abstract

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

BIOTIN AS A GROWTH REQUIREMENT FOR BLASTOMYCES DERMATITIDIS

“…biotin compared with that of the parent strain. They proved to be similar to the parent, thus eliminating any further consideration of a mutation to "autotrophism" (Leonian and Lilly, 1943).…”

Effects of Certain Limiting Conditions on the Synthesis of B Vitamins by Yeast

“…In making a critical study of the changes in the vitamin content of yeast cultured in the presence of inhibitors, it is necessary to recognize that an observed lowering in content may be interpreted as arising from (1) a diminished need for, (2) an interference in the synthesis of, (3) a lessened retention of, or (4) in some cases, a reduced absorption from the medium of that vitamin. An observed increase may be regarded as evidence for (1) an enhanced requirement, (2) a stimulation of synthesis, (3) an increased retention, or (4) in some cases, an increased absorption from the medium.…”

“…these substances by the orgamsm is the basis for their dispensability. Leonian and Lilly (2), who also used a strain of yeast isolated from a Fleischmann's cake, reported that by successively subculturing this yeast in a medium from which first pantothenic acid and then pantothenic acid and biotin were omitted a variant was obtained which grew well in a medium containing none of the B 61…”

Yeast Genetics 1

“…In the backcross in which both parents were incapable of synthesizing either pantothenic acid or biotin, the fact that the progeny were generally inferior suggests that adaptations do not seriously complicate the interpretation. Leonian and Lilly (28,29,30) derived yeasts capable of synthesizing vtamins from cultures incapable of performing the syntheses. Their procedure probably favored the selection of mutations.…”