A Direct Relationship Between Pantothenate Concentration and the Time Required to Induce the Production of Pantothenate-Synthesizing "Mutants" in Yeast

Abstract

This paper describes experiments indicating that the concentration of pantothenate bears a direct relation to the time required to restore pantothenate synthesis in a yeast cell. Various members of the pedigree shown in Table 112 were grown in batches of Burkholder's medium made up with the following amounts of pantothenate added per liter: .100, 50, 20, 10, 5, 2, 1, 0.5, and 0 y. Each tube was inoculated in a uniform manner with a loop. Three. hundred colonies grew from each loopful of cells on plating, but since thehaploid cells were typically :aggregated the total number of cells was probably less than 1500. Figure 3 shows the results with S. cerevisiae (culture No. 1), the turbidity being plotted against time in hours. The graphs are made by plotting the average of. the turbidity produced in duplicate tubes, except in a few cases in which the tubes were. so widely different that averaging did not seem to be a permissible practice. Usually the readings differed by only a few units and averaging was obviously acceptable. After 45 hours, growth is practically completed in the media containing 50 and 100 y of pantothenate, but it is fully 75 hours before appreciable growth is recorded in the tube without the added pantothenate. This culture had previously been characterized as a synthesizer of pantothenate. These data show that diagnosis depends largely on the time at which readings are taken. Comparison of the 100 y and O y tubes at the end of 45 hours would have resulted in characterizing this particular organism as a nonsynthesizer of pantothenate. The relationship between the amount of added pantothenate and the time at which growth begins is quite clear, since the curves are all closely parallel *during early and logarithmic growth and overlapping occurs only after the logarithmic phase of growth has been completed. There is a sharp difference between the time at which growth begins in the tubes containing 0.5 and 1 y of pantothenate per liter as well as between growth in tubes containing 1 and 2 y of pantothenate per liter. The culture of S. cereishiae, whose reactions are recorded in fig. 3, was induced to sporulate, and similar tests with the four haplophase cultures are shown in figs. 4 and 5. Cultures No. 3 and No. -4 are remarkably similar in behavior. .According to previous techniques, these would have been classified as nonsynthesizers because growth in the absence of pantothenate did not beginuntil after *250 hours. The particularly interesting feature of the behavior of these cultures is the direct relation between the length of the delay before growth begins and concentration of pantothenate in the medium.