Towards understanding the evolution of the human commensal yeast Candida albicans

Allelic frequencies and relationships for one dimorphic locus and three unlinked polymorphic loci have been determined for 114 unrelated isolates of Candida albicans, including 14 laboratory reference strains and 50 strains from each of two geographic regions. Although there was no indication of geographical partitioning, there were significant correlations for specific allelic pairs among loci and little evidence that any alleles were in Hardy-Weinberg equilibrium. This gives additional support for the concept that the primary mode of genetic inheritance in this species is clonal, with other intracellular genetic events playing a lesser role in the creation of genomic diversity. Through inference of this and other known attributes of closely related Candida species, such as sequence analysis of IS1 and the ITS2 (internal transcribed spacer 2) region of the rDNA cistron, the deduced phylogeny suggests an evolutionarily recent origin for many frequently isolated strains. This finding will be of interest in the context of understanding pathogenicity and drug resistance in this human commensal yeast.