Variation of colony morphology and chromosomal rearrangement in Candida tropicalis pK233.

UV irradiation treatment of the asexual yeast Candida tropicalis gave rise to morphological mutants exhibiting at least four different types of abnormal colonies on glucose-containing solid medium. These mutants were named according to their colony morphologies: 'doughnut', 'frilly', 'echinoid' and 'walnut' mutants. The doughnut mutant produced a wrinkled colony with a hollow in its central region that was rich in filamentous pseudohyphal cells. With increased incubation time, the colony gradually changed to a reticulate shape. The parent strain, which normally produced smooth colonies, gave similar colonies to those of the doughnut mutant when grown in medium containing oleic acid as carbon source. Both the frilly and the walnut mutants produced pseudohyphal cells in a similar fashion to the doughnut mutant. The echinoid mutant produced an echinulate colony morphology with aerial hyphae and contained true hyphal cells as well as pseudohyphal ones. Pulsed-field gel electrophoresis showed that the echinoid and frilly mutants had different karyotypes from that of their parent strain, suggesting the occurrence of chromosomal rearrangements associated with these morphological mutations.