Infrequent genetic exchange and recombination in the mitochondrial genome of Candida albicans

Previous analyses of diploid nuclear genotypes have concluded that recombin ation has occurred in populations of the yeast Candida albicans, To address the possibilities of clonality and recombination in an effectively haploid genome, we sequenced seven regions of mitochondrial DNA (mtDNA) in 45 stra ins of C. albicans from human immunodeficiency virus-positive patients in T oronto, Canada, and 3 standard reference isolates of C. albicans, CA, CAI4, and WO-1. Among a total of 2,553 nucleotides in the seven regions, 62 poly morphic nucleotide sites and seven indels defined nine distinct mtDNA haplo types among the 48 strains. Five of these haplotypes occurred in more than one strain, indicating clonal proliferation of mtDNA, Phylogenetic analysis of mtDNA haplotypes resulted in one most-parsimonious tree, Most of the nu cleotide sites undergoing parallel change in this tree were clustered in bl ocks that corresponded to sequenced regions. Because of the existence of th ese blocks, the apparent homoplasy can be attributed to infrequent, past ge netic exchange and recombination between individuals and cannot be attribut ed to parallel mutation, Among strains sharing the same mtDNA haplotypes, m ultilocus nuclear genotypes were more similar than expected from a random c omparison of nuclear DNA. genotypes, suggesting that clonal proliferation o f the mitochondrial genome was accompanied by clonal proliferation of the n uclear genome.