MOLECULAR MARKERS REVEAL THAT POPULATION-STRUCTURE OF THE HUMAN PATHOGEN CANDIDA-ALBICANS EXHIBITS BOTH CLONALITY AND RECOMBINATION

The life history of Candida albicans presents an enigma: this species is thought to be exclusively asexual, yet strains show extensive pheno typic variation, To address the population genetics of C. albicans, we developed a genetic typing method for codominant single-locus markers by screening randomly amplified DNA for single-strand conformation po lymorphisms, DNA fragments amplified by arbitrary primers were initial ly screened for single-strand conformation polymorphisms and later seq uenced using locus-specific primers, A total of 12 single base mutatio ns and insertions were detected from six out of eight PCR fragments, P atterns of sequence-level polymorphism observed for individual strains detected considerable heterozygosity at the DNA sequence level, suppo rting the view that most C. albicans strains are diploid, Population g enetic analyses of 52 natural isolates from Duke University Medical Ce nter provide evidence for both clonality and recombination in C. albic ans, Evidence for clonality is supported by the presence of several ov errepresented genotypes, as well as by deviation of genotypic frequenc ies from random (Hardy-Weinberg) expectations, However, tests for nonr andom association of alleles across loci reveal less evidence for link age disequilibrium than expected for strictly clonal populations, Alth ough C, albicans populations are primarily clonal, evidence for recomb ination suggests that sexual reproduction or some other form of geneti c exchange occurs in this species.