Dimorphism in a new isolate of Saccharomycopsis Schiönning

Abstract

Two strains of Saccharomycopsis guttulata Robin (Schiönning) were isolated from two out of four specimens of Lepus californicus, the wild jack rabbit of California. One isolate was similar to typical strains with budding cells occurring in domestic rabbits. The second strain was atypical in being dimorphic. Colonies of the yeast form, consisting of budding cells, were smooth and glistening, while those of the filamentous form were irregular, rough, and dull. The filamentous form consisted of septate, branched hyphae, radiating from a central origin of growth. New filaments generally were initiated by fragmentation. The two new strains were similar to domestic strains in assimilation and fermentation reactions and grew only between 30 and 40C. Both strains formed ascospores at 18C. The filamentous strain, unlike other S. guttulata strains, was not carbon dioxide dependent at 37C but did require oxygen. At 30C it became carbon dioxide dependent. During the stationary phase, a morphogenetic change occurred from the filamentous form to a yeast form, which was stimulated by anaerobic conditions. The budding form of the filamentous strain was relatively stable in culture and at either 30 or 37C it was carbon dioxide dependent. Spontaneous reversions from the budding to the filamentous form appear to occur sporadically.