CORRELATION BETWEEN POLYPLOIDY AND AUXOTROPHIC SEGREGATION IN THE IMPERFECT YEAST CANDIDA-ALBICANS

In order to clarify the relationship between polyploidization and the capability of phenotypic switching in the imperfect yeast Candida albi cans, two types of variants were isolated as segregants from a fusant, which produced a proportion of the cell population with a higher ploi dy than the rest, either in a temperature-dependent or -independent ma nner, when incubated at low (28 degrees C) and high (37 degrees C) tem peratures. In the case of the temperature-dependent type of variants, high-ploidy cells appeared at 37 degrees C but rarely at 28 degrees C. This phenotype was named Pld(ts) (temperature-sensitive polyploidizat ion), and the temperature-independent phenotype was called Pld(-). The appearance of high-ploidy cells in the culture of the Pld(ts) strain at 37 degrees C was accompanied by a significant increase in the frequ ency of auxotrophic variants; these variants probably occur as a resul t of segregation of auxotrophic markers from the heterozygous to the h omozygous state. Both Pld(ts) and Pld(-) phenotypes were recessive in a fusion with a Pld(+) parent. An adenine auxotrophic marker (ade1) wa s introduced into a Pld(ts) strain in a heterozygous state, and the in dividual high-ploidy cells of this strain, grown at 37 degrees C, were micromanipulated to form colonies, which consisted of red and white s ectors appearing at high frequency on a pink background. When the ade1 auxotrophy was introduced into Pld(-) strains, frequently sectored co lonies were produced. These results suggested an increased level of ch romosome missegregation in both types of Pld mutants. Analyses by puls ed-field gel electrophoresis of Ade(-) segregants, derived from a micr omanipulated high-ploidy cell of a Pld(ts) strain, suggested the occur rence of nonreciprocal recombination, some of which includes chromosom e loss.