Occurrence of ploidy shift in a strain of the imperfect yeast Candida albicans.

A clinical isolate of Candida albicans, a member of the Fungi Imperfecti, was polyploid as shown by the fact that it contained two kinds of nuclei, one of diploid and one of tetraploid DNA content. These determinations were made by fluorescence microscopy-photometry. The nucleus-associated organelles (NAOs), or spindle pole bodies, of yeast cells in this isolate were classified into two groups, one diploid and the other tetraploid, according to their dimensions as determined by serial thin-sectioning electron microscopy. A ploidy shift from diploid to tetraploid was found in individual cells of a culture of this isolate undergoing diphasic growth in minimal salts medium. A process of shift-down or reduction of ploidy from tetraploid to diploid was also observed by electron microscopy during these growth conditions: this appeared to occur in large cells which showed multiple spindle formation during nuclear division, a phenomenon apparently similar to the process of meiosis II during sporogenesis of Saccharomyces cerevisiae, but differing in that it produces diploid daughter nuclei by the vegetative process.