Dissociation in Yeasts

Abstract

In an attempt to revive a desiccated culture of Saccharomyces cerevisiae Hansen, Saaz strain, a culture of diplococcus was obtained. On serial transfer in malt extract broth, this diplococcus form was gradually changed back into the original yeast form. Single cell isolations of the following yeasts were made: S. cerevisiae (Froberg strain), S. ellipsoideus Hansen, Willia anomala, and Zygosaccharomyces mandshuricus. Cultures from these single cell isolations were then aged and serially transferred to LiCl broth, to brilliant green broth, and to malt extract broth containing different % of ethyl alcohol, and were also desiccated on gypsum blocks and incubated at various temps. in malt extract broth. Smooth (S), rough (R), gonidial (G), and transitional (T) forms appeared constantly. The S form is the normal form described in the literature for most species, and possesses the morphological, physiological and cultural characteristics usually ascribed to the species. The R form of the yeast consists of greatly elongated cells which form dull rugose, wrinkled colonies having a filamentous edge under low power magnification. The physiological properties of the R form are the same as those of the S form. The G form consists of very small cells. They are asporogenic, differ somewhat from the S and R forms in the sugars fermented, and produce an acid instead of an alcoholic fermentation. All the G forms except one liquefied gelatin. On initial isolation they grow slowly, producing colonies microscopic in size at the end of a week''s incubation. When they became adapted to their environment, they produced a thin spreading colony. The T form, which is the transitional form between the S or R forms and the G form, consists of a highly refractile cell which produces the G form by the formation of a large number of minute buds on the periphery of the cell. The T form has never been cultured but has been observed repeatedly in hanging drop preparations. After the R and G forms had been obtained and single cell isolations maxle from them, it was possible to revert them to the original S form by rapid transfer in malt extract broth. The R and G forms are fairly stable; cultures of these forms have remained in their original form for approximately a yr., with little tendency to revert to the original S form. In some cases certain variants were obtained, such as pink S forms which became mucoid; certain black R forms; and one G form which produced a bright orange-colored colony. Limited immunological studies indicate a closer relationship between the R and G forms than between the S form and these 2 forms. The production of these various forms clarifies some points in connection with yeasts which have remained obscure such as scum production, certain defects in beer and unsatisfactory yields in the production of industrial alcohol. It is likewise evident that alcoholic production which is associated with true yeasts is absent and is replaced by acid production in the G form of the true yeast. Likewise the G forais of all the yeasts studied liquefied gelatin, except in one case, while the S and R forms did not.