Abstract
We applied multilocus sequence typing (MLST) to investigate the population structure and mode of reproduction of Cryptococcus neoformans var. grubii (serotype A). This MLST system utilizes 12 unlinked polymorphic loci, which are dispersed on nine different chromosomes, and allows the unambiguous identification of closely related strains of serotype A. We compared MLST analyses with the conventional genotyping method of detecting amplified fragment length polymorphisms (AFLPs), and there was excellent correlation between the MLST and AFLP results. However, MLST differentiated a larger number of strains. We analyzed a global collection of isolates of serotype A using both methods, and the results identified at least three genetically distinct subpopulations, designated groups VNI, VNII, and VNB. Groups VNI and VNII are widespread, dominated by isolates with the MATalpha mating type, and predominantly clonal. Conversely, isolates of group VNB are unique to Botswana, include a significant proportion of fertile strains with the MATa mating type, and manifest compelling evidence of recombination. We have AFLP genotyped >1000 strains of serotype A from different parts of the world, including isolates from several African countries, and, to date, haploid serotype A isolates of group VNB have been found only in Botswana.
Highlights
C RYPTOCOCCUS neoformans is a pathogenic yeast that causes debilitating disease of the central nervous system and other organs in humans
The genome of C. neoformans var. grubii contains the machinery for sexual reproduction and recombination, and strains are capable of undergoing both processes in the laboratory, the overwhelming majority of natural isolates possess only one mating-type allele, MATa, and exhibit significant evidence of clonality
Litvintseva et al (2005) analyzed multilocus amplified fragment length polymorphism (AFLP) genotypes of .700 environmental and clinical isolates of C. neoformans serotype A from the United States and detected linkage equilibrium among the loci in the individual subgroups, which could be attributed to recombination in these subgroups
Summary
C RYPTOCOCCUS neoformans is a pathogenic yeast that causes debilitating disease of the central nervous system and other organs in humans. Grubii contains the machinery for sexual reproduction and recombination, and strains are capable of undergoing both processes in the laboratory, the overwhelming majority of natural isolates possess only one mating-type allele, MATa, and exhibit significant evidence of clonality. Burt et al (2000) analyzed multilocus genotypes of 222 serotype A isolates from the United States and detected no significant linkage disequilibrium among the loci, which may indicate evidence of recombination in the population. Litvintseva et al (2005) analyzed multilocus amplified fragment length polymorphism (AFLP) genotypes of .700 environmental and clinical isolates of C. neoformans serotype A from the United States and detected linkage equilibrium among the loci in the individual subgroups, which could be attributed to recombination in these subgroups. The global population was separated into two genetically distinct groups, and these two groups differed from the subgroups in Botswana
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