UPTAKE OF NUTRIENTS BY YEASTS I. PENETRATION OF SUGARS INTO YEASTS

Abstract

The ability of representative yeasts to take up selected mono-, di- and trisaccharides has been examined, employing in the first instance sugars not utilized for growth. The yeasts took up most monosaccharides, though to varying extents which seldom attained but often approached the theoretical amount. Contrary to previous ideas, sugars appear to be absorbed in cell sap and probably reach this site by diffusion. Di- and trisaccharides penetrated the cells to only a very limited extent and it was found, using radioactive maltose as a readily-detected marker, that four selected species of yeast undergoing division failed almost completely to remove maltose from the growth medium. The results show that yeasts which do not utilize oligosaccharides such as maltose have an impediment to the entry of these sugars, possibly owing to the limiting pore size of the cell wall. However, by employing a brewing yeast potentially capable of utilizing maltose but de-adapted to maltose fermentation, evidence was gained to show that the mechanism by which maltose enters such yeasts as are used in brewing appears not to be simple diffusion but an adaptive process linked to its utilization.