Highly recombinant VGII Cryptococcus gattii population develops clonal outbreak clusters through both sexual macroevolution and asexual microevolution.
Bottom Line: We found that VGIIa/b/c populations show evidence of clonal expansion in the PNW.We also found that the genomes of two basal VGII isolates from HIV(+) patients contain an introgression tract spanning three genes.This work shows that multiple processes can contribute to the emergence of an outbreak.
Affiliation: Department of Molecular Genetics and Microbiology, Duke University Medical Center, Durham, North Carolina, USA firstname.lastname@example.org.Show MeSH
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Mentions: While strains within each of the five clonal clusters of C. gattii are highly related to each other, comparisons among clusters revealed substantial differences. However, the sites differentiating these clusters were not uniformly dense across the genome. This is demonstrated by incongruity between phylogenies inferred from different portions of the genome (Fig. 5), suggesting that ancestral recombination among the clonal lineages has resulted in some portions of the genome being more similar between two clonal groups than the others. Further evidence is provided by examining SNP density between isolates. This analysis demonstrates the presence of islands of identity between any two individual isolates where diversity is considerably lower than the genome-wide average (Fig. 6A). Inferring phylogenies from these regions of depressed polymorphism reveals uniquely close relationships among strains (Fig. 6B). This suggests that sexual reproduction likely contributed to the production of the ancestor of each clonal cluster, with subsequent mitotic clonal expansion of these isolates to spread throughout the environment. Notably, none of the outbreak clusters has an individual partner strain or cluster that contributes a large portion of the genome (i.e., 50% for one cross, 25% for two crosses, etc.). This suggests that either sampling has captured only a small portion of the VGII population or some of these intermediate strains may no longer exist.
Affiliation: Department of Molecular Genetics and Microbiology, Duke University Medical Center, Durham, North Carolina, USA email@example.com.