Protoplasts fusion hybrids from Candida albicans morphological mutants.

Three pairs of strains, derived from Candida albicans 1001 (wild type) and carrying appropriate selection markers, were crossed by means of protoplast fusion. The corresponding fusion products were regenerated in selection medium and hybrids of rapid growth and more defined characteristics were eventually isolated and analyzed for relevant properties. Hybrids from a cross of two auxotrophic strains with no morphological alteration had a normal morphology but gave rise to rough-filamentous segregants of mostly pseudomycelial appearance, probably through DNA content reduction. The observation was consistent with a previous suggestion that C. albicans 1001 carries recessive mutant alleles that can be unmasked. A permanently filamentous strain (Y- phenotype) when crossed with a mycelium deficient (F-) strain gave rise to wild-type hybrids with a normal capacity for mycelium formation. Finally, two Y- strains, with similar phenotypes consisting of rough colony formation and mostly pseudomycelial morphology of cells under all conditions, also complemented since they gave rise to wild-type hybrids. It is concluded that the determinants of the mutant phenotype must be different in these two strains.