Variation in the electrophoretic karyotype analysed by the assignment of DNA probes in Candida albicans

By using pulsed-field gel electrophoresis, we have separated the entire chromosome bands and examined the electrophoretic karyotypes of 27 strains of Candida albicans. The electrophoretic karyotype varied widely among these strains. Their chromosomal DNAs were resolved into 7-12 bands ranging in size from 0.42 to 3.0 Mb. Most of the separated chromosomal bands were assigned by eight cloned C. albicans DNA probes. These results suggest that the haploid number of C. albicans chromosomes is eight. Each of the probes hybridized specifically to one or two bands of similar size in most strains. With the exception of the MGL1 probe, when two bands were detected by one probe, the size of one of them was very conserved whilst the other was of fairly variable size. The sizes of the chromosome bands assigned by the MGL1 probe were much more variable. As C. albicans is considered to be a diploid organism, it is inferred that the karyotype polymorphism between strains is mainly derived from wide size heterogeneity in one of the homologous chromosomes. Furthermore, we have confirmed species-specific and strain-specific variation in medically important Candida species (C. stellatoidea, C. tropicalis, C. parapsilosis, C. krusei, C. guilliermondii, C. kefyr and C. glabrata). Electrophoretic karyotype analysis is thus useful for species assignation. The TUB2 probe, encoding C. albicans beta-tubulin, hybridized to the chromosomal DNA of all the Candida species examined, but four C. albicans probes exhibited cross-species hybridization with C. stellatoidea only. The karyotype of C. stellatoidea seems to be within the range of the intraspecies variation observed in C. albicans.