High‐frequency occurrence of chromosome translocation in a mutant strain of Candida albicans by a suppressor mutation of ploidy shift

Significant occurrence of high-ploidy cells is commonly observed among many Candida albicans strains. We isolated two isogenic strains, STN21 and STN22, each from a half sector of a colony obtained after mild UV-irradiation of a Arg(-) derivative of CBS5736. The two strains were different from each other in ploidy states and chromosome organization. Although cells of STN22 were homogeneous in size and had a single nucleus, high-ploidy cells, with either a single large nucleus or several nuclei, were present together with apparently normal cells with a single nucleus in the cell population of STN21. Flow cytometry showed that STN22 was a stable diploid; however, STN21 seemed to be the mixture of different ploidy states, including diploid and tetraploid. The phenotype of STN21 containing high-ploidy cells is referred to here as the Sps(-) phenotype (suppressor of ploidy shift). STN22 showed a typical electrophoretic karyotype similar to strain 1006 in C. albicans. However, an extra chromosomal band appeared in some clones of STN21 at high frequency. By assignment of several DNA probes, this extra chromosome was shown to be a translocation of the 7F-7G portion of chromosome 7 with the 470 kb DNA segment containing H SfiI fragment from chromosome 4. Thus, this extra chromosome is a hybrid of 4H and 7F-7G. Since the isogenic Sps(+) strain STN22 exhibited no extra chromosome bands, a correlation is suggested between the Sps(-) phenotype and the occurrence of chromosome translocations. Copyright (C) 2000 John Wiley & Sons, Ltd.