Can yeast grow in a chemically pure medium?

Abstract

Reports have lately appeared that yeast can grow on a medium composed of known ingredients, viz.: 50 grams cane sugar (Domino brand), 2 grams KH₂ PO₄, 2.35 grams (NH₄)₂ SO₄, 0.25 gram CaCl₂ and 0.25 gram MgSO₄, dissolved in a liter of distilled water. It was claimed that on the above medium, which we will call medium O, yeast could be grown in sufficient quantities to serve as a source of vitamine B in animal feeding experiments.

We have attempted to grow yeast on the above medium but have found it difficult to obtain sufficient yeast by this method. It grew very slowly in the incubator and hardly at all at room temperature. The yields were very small; for example, 1800 c.c. of nutritive solution distributed in twelve flasks gave, after growing for a month, 1.5 grams of dried yeast, whereas on addition of 1 c.c. autolyzed yeast to each flask, 900 c.c. in six flasks gave in four days 3 grams of product. Whereas the yeast in the first case developed a brown pigment and presented a spore-like shrunken appearance, in the second case the cells were colorless and in active budding.

In sub-culturing the yeast obtained on medium 0, by introducing 5 c.c. into each of a series of flasks containing fresh media, the yield remained almost constant. This excluded the cause of the growth as being due to vitamine D introduced with the seeding, and suggested the possibility of an impurity in the medium. It therefore became necessary to investigate more carefully the purity of one or more of the three constituents of the medium, namely, salts, water and cane sugar.

Each one of the salts used as well as the cane sugar was dissolved separately in distilled water, shaken out with fullers earth and the filtrate evaporated to dryness.