The Biochemical Classification of Yeast Strains.

The classification of yeasts has been based to some degree on their ability to ferment certain sugars. This test is one of the well-established biochemical methods. Stelling-Dekker (1931) systematically examined the genus Saccharomyces and reorganized its classification unequivocally upon fermentation ability. However, this system, good though it be, is inadequate for the classification of the great number of yeast strains which, because of fermentative ability, must be called either Saccharomyces cerevisiae or Saccharomyces carlsbergensui. Designation of cultures as sub-species, varieties, strains and races is often based on individual characteristics which are evident in a particular process. The microbiologist is seldom able to identify exactly a fresh isolation or an unknown culture and must perforce carry it in his collection with a numerical designation. Although this inability may not be a great hindrance to industry, it is a serious problem for microbiology. The study of growth factors in particular has been greatly hindered by the lack of sharp differentiation between cultures. As briefly reported elsewhere, Schultz, Atkin and Frey (1938-9) found a growth reaction which permits a sharp differentiation between otherwise closely related varieties of yeast. This difference appears in both the S. cerevisiae and S. carlsbergensis groups and does not appear to be related to the size or shape of cells so far as we have been able to determine.