The Fermentation of Trehalose by Yeasts and its Taxonomic Implications

SUMMARY: In the classification of yeasts it is customary to use an infusion of bakers’ yeast as the basal medium for fermentation tests. This extract frequently contains variable amounts of trehalose. A number of yeasts were observed to ferment yeast extract and trehalose. The fermentation of yeast extract is serious from a taxonomic point of view, since it gives the impression of positive fermentation of a sugar which actually may not be fermentable. Dilute yeast autolysate should be used as the basal fermentation medium since during autolysis trehalose is destroyed. The fermentation of yeast extract (without added sugar) is easily observed in Durham tubes by the collection of gas in the inserts, but when Einhorn fermentation tubes are used gas production is seldom apparent. One culture (N-18) isolated from spoiled apricots, and identified as Candida tropicalis showyed adaptive trehalose fermentation. The ability of various yeasts to ferment trehalose was investigated, using 133 cultures, representing twenty genera and seventy-three species. Sixteen species representing seven genera fermented yeast extract and trehalose. The fermentation of trehalose is worthy of consideration as a character for use in differentiating certain species of Candida, and perhaps other yeasts.