Cell-wall structure,mitosis and urease activity in Torulopsis species of high GC content

Five Torulopsis species, in which, characteristically, the mean molar percentage of guanine plus cytosine of the DNA bases (GC content) is above 50%, were examined to determine their cell-wall structure; the mode of bud formation; course of mitosis and their urease activity. The two urease-negative species, T. gropengiesseri (% GC 57.1) and T. silvatica (% GC 56.3), were found to possess affinitive properties which characterize perfect ascomycetous yeast species. In the urease-positive species, T. fujisanensis (% GC 65.0–66.1), T. ingeniosa (% GC 55.6) and T. philyla (% GC 63.9), there appeared to be a correlation between pronounced urease activity and the affinitive properties which characterize perfect basidiomycetous yeast species. Pronounced urease activity has, however, also been found in the ascomycetous species Schizosaccharomyces pombe. Consequently neither high GC ratios nor the presence of urease activity when considered individually, can be taken as reliable criteria when attempting to establish the affinity of yeasts the perfect states of which are not known, with the Basidiomycetes. A strain of the ascomycetous species Sclerotinia trifoliorum was examined by electron microscopy for comparative purposes.