Comparative gene genealogical analyses of strains of serotype AD identify recombination in populations of serotypes A and D in the human pathogenic yeast Cryptococcus neoformans

Abstract

Cryptococcus neoformans is a major pathogen of humans throughout the world. Using commercial monoclonal antibodies to capsular epitopes, strains of C. neoformans manifest five serotypes: A, B, C, D and AD. Previous studies demonstrated significant divergence among serotypes A, B, C and D, which are typically haploid. In contrast, most strains of serotype AD are diploid or aneuploid and result from recent hybridization between strains of serotypes A and D. Whether serotypes A, B, C and D represent strictly asexual lineages is not known. Using comparative genealogical analyses of two genes, the authors investigated whether recombination occurred among strains within serotypes A and D. For each of 14 serotype AD strains, a portion (642 bp) of the orotidine monophosphate pyrophosphorylase (URA5) gene was cloned and sequenced. Each of these 14 strains contained two different alleles and sequences for both alleles were obtained. The URA5 gene genealogy was compared to that derived from the laccase (LAC) gene, which was reported recently for the same 14 strains. For both genes, each of the 14 serotype AD strains contained two phylogenetically distinct alleles: one allele was highly similar to those from serotype A strains and the other to alleles from serotype D strains. However, within both the serotype A allelic group and the serotype D allelic group, there was significant incongruence between genealogies derived from URA5 and LAC. The results suggest recombination in natural populations of both serotypes A and D.

Long-distance dispersal and recombination in environmental populations of Cryptococcus neoformans var. grubii from India

“…The reconstructed serotype A and D populations both showed evidence of recombination (Xu & Mitchell, 2003). The second example was from humans in Botswana, where both mating types were found and, not surprisingly, evidence for recombination as well (Litvintseva et al, 2003).…”

Spores as Infectious Propagules ofCryptococcus neoformans

“…We hypothesize that there could be serotype differences in the virulence patterns between spores from serotypes A and D. Sukroongreung et al previously conducted experiments with serotype D spores, whereas all of our virulence studies were conducted with serotype A spores. These serotypes are now recognized as distinct species that diverged 18.5 million years ago (32,56), so they may differ in virulence. There could also be host species-specific differences such that spores are more infectious than yeast cells in humans but not in mice.…”

Multiple gene genealogical analyses suggest divergence and recent clonal dispersal in the opportunistic human pathogen Candida guilliermondii

“…The primers and the expected PCR product size for all five gene fragments are presented in Table 2. PCR amplification was performed according to standard protocols (Xu et al, 2002(Xu et al, , 2000bXu & Mitchell, 2003b). PCR products were cleaned using the microCLEAN purification kit (Qiagen) and sequenced using both the forward and reverse primers using an ABI3100 automated DNA sequencer (MoBix Laboratory, McMaster University).…”

“…Gene genealogical analyses have been used to address a variety of ecological and evolutionary genetic issues, including the rates of dispersal, hybridization and divergence, and the role of clonality and recombination in the structure of fungal populations (Xu, 2006;Xu et al, 2002Xu et al, , 2005Xu & Mitchell, 2003b). Given a group of clonally reproducing organisms, the genealogies of multiple genes are expected to be the same, since evolutionary changes arise mainly through independent mutations.…”