The Isolation of Yeasts from Soil

SUMMARY: A series of comparative studies was made of soil yeasts in a yellow-brown earth originally under forest but now under pasture. Of six solid acid media used for primary isolations, an agar medium containing 4% (w/v) glucose and 1% (w/v) peptone gave the highest yeast counts. Two soil-extract agars and a modified Czapek-Dox agar gave slightly lower counts; a third soil-extract agar inhibited all but one yeast species and gave a much decreased count. The addition of a surface active agent to glucose peptone agar did not increase the count. Acid broth enrichment cultures gave a distorted picture of the species pattern shown by primary cultures on solid media. Prolonged mechanical shaking of soil dilutions before culturing, and the addition of a surface active agent to the diluent did not affect the yeast pattern seen, quantitatively or qualitatively.