Cryptococcus neoformans population includes hybrid strains homozygous at mating-type locus (original) (raw)
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Determination of Cryptococcus neoformans var. neoformans mating type by multiplex PCR
Clinical Microbiology and Infection, 2004
Mating type plays an important role in the epidemiology and virulence of Cryptococcus neoformans. The present study designed a multiplex PCR method to distinguish the six mating type patterns (Aa, Da, Aa, Da, Aa ⁄ Da, and Aa ⁄ Da) of C. neoformans var. neoformans. PCR amplification identified one fragment for Aa (860 bp), Da (413 bp) and Da (645 bp) strains, two fragments for Aa (320 and 400 bp) and Aa ⁄ Da (860 and 413 bp) strains, and three fragments (645, 400, 320 bp) for an Aa ⁄ Da strain. The method appears to be a valid, simple and relatively inexpensive tool for epidemiological and virulence studies.
Infection and Immunity, 2001
Cryptococcus neoformans is a pathogenic basidiomycete with a defined sexual cycle involving mating between haploid yeast cells with a transient diploid state. C. neoformans occurs in four predominant serotypes (A, B, C, and D), which represent different varieties or species. Rare clinical and environmental isolates with an unusual AD serotype have been reported and suggested to be diploid. We found by fluorescence-activated cell sorter analysis that serotype AD strains are aneuploid or diploid. PCR analysis with primers specific for serotype A or D alleles of the CNA1 , CLA4 , and GPA1 genes revealed that both alleles are often present in serotype AD strains. PCR analysis with primers specific for genes in the MAT a or MAT α mating-type loci revealed that serotype AD strains are heterozygous for the mating-type locus. Interestingly, in several serotype AD strains, the MAT α locus was derived from the serotype D parent and the MAT a locus was inherited from a serotype A parent that h...
Variability of karyotypes and RAPD types in genetically related strains of Cryptococcus neoformans
Current Genetics, 1997
Variation in karyotypes and RAPD patterns of genetically related strains of Cryptococcus neoformans were analyzed. Capsular and filamentous mutants usually differ in their karyotypes from wild-types, but the RAPD patterns were found to be similar. Karyotype differences were observed in most heterothallic matings, but RAPD patterns remained identical. After self-sporulation of a diploid strain, minor chromosomal length polymorphism and minor changes in the RAPD types occurred. Three mechanisms, either alone or in combination, may in varying degrees contribute to the karyotype variation of C. neoformans: (1) mitotically induced changes; (2) karyotype changes as a result of meiotic recombination, and (3) mutagen-induced changes. The present data do not support the meiotic maintenance hypothesis, which claims that the amount of CLP generated is inversely proportional to the frequency of meiosis.
Journal of Clinical Microbiology, 2002
To better understand the epidemiology and population structure of Cryptococcus neoformans , we determined mating types for 358 C. neoformans strains isolated through the active surveillance program from 1992 to 1994 in four geographic areas in the United States: San Francisco, California; Georgia; Texas; and Alabama. Two assays were used to determine mating types: (i) crossing with standard laboratory tester strains JEC20 and JEC21 on V8 agar medium; and (ii) PCR with the mating type α allele-specific primer of the STE12 gene and with serotype (A and D)- and mating type (a and α)-specific primers of the STE20 gene. Using these two methods, we found that this sample consisted of the following: (i) 324 serotype A, mating type ( MAT ) α (Aα) strains; (ii) 12 serotype D, α (Dα) strains; (iii) 14 serotype AD strains with mating type alleles Aa and Dα (AaDα); (iv) 2 serotype AD strains with mating type alleles Aα and Da (AαDa); (v) 3 serotype B, α (Bα) strains; and (vi) 3 serotype AD stra...
Pathogens
Hybrids between Cryptococcus neoformans and Cryptococcus deneoformans are commonly found in patients and the environment. However, the genetic stability of these hybrids remains largely unknown. Here, we established mutation accumulation lines of a diploid C. neoformans × C. deneoformans laboratory hybrid and analyzed the genotypes at 33 markers distributed across all 14 chromosomes. Our analyses found that under standard culture conditions, heterozygosity at most loci was maintained over 800 mitotic generations, with an estimated 6.44 × 10−5 loss-of-heterozygosity (LoH) event per mitotic division. However, under fluconazole stress, the observed LoH frequency increased by > 50 folds for the two markers on Chromosome 1, all due to the loss of the fluconazole susceptible allele on this chromosome. Flow cytometry analyses showed that after the 40th transfer (120 days), 19 of the 20 lines maintained the original ploidy level (2N), while one line was between 2N and 3N. The combined fl...
Multiple origins of hybrid strains of Cryptococcus neoformans with serotype AD
Microbiology (Reading, England), 2002
Cryptococcus neoformans is a major pathogen of humans throughout the world. Using commercial mAbs to capsular epitopes, strains of C. neoformans manifest five distinct serotypes--A, B, C, D and AD. Previous studies demonstrated significant divergence among serotypes A, B, C and D, which are thought to be haploid. In this study the origins and evolution of strains of serotype AD were investigated. A portion (537 bp) of the laccase gene was cloned and sequenced from 14 strains of serotype AD. Each strain contained two different alleles and sequences for both alleles were obtained. These sequences were compared to those from serotypes A, B, C and D. This analysis indicated that each of the 14 serotype AD strains contained two phylogenetically distinct haplotypes: one haplotype was highly similar to the serotype A group and the other to the serotype D group. To explain the origins of these serotype AD strains, genealogical analysis is consistent with at least three recent and independen...
1999
Cryptococcus neoformans var. gattii lives in association with certain species of eucalyptus trees and is a causative agent of cryptococcosis. It exists as two mating types, MAT␣ and MATa, which is determined by a single-locus, two-allele system. In the closely related C. neoformans var. neoformans, the ␣ mating type has been found to outnumber its a counterpart by at least 30:1, but there have been very limited data on the proportions of each mating type in C. neoformans var. gattii. In the present study, specific PCR primers were designed to amplify two separate ␣-mating-type genes from C. neoformans var. gattii strains. These were used to survey for the presence of the two mating types in clinical and environmental collections of C. neoformans var. gattii strains from Australia. Sixty-eight of 69 clinical isolates produced both ␣ mating type-specific bands and were assumed to be of the ␣ mating type. The majority of environmental isolates were also of the ␣ mating type, but the a mating type was located in two separate areas. In one area, the a mating type outnumbered the ␣ mating type by 27:2, but in the second area, the ratio of the two mating types was close to the 50:50 ratio expected for sexual recombination.
Genetics, 2007
Cryptococcus neoformans has two varieties, var. grubii and var. neoformans, that correspond to serotypes A and D, respectively. Molecular phylogenetic analyses suggest that these two varieties have diverged from each other for ∼18 million years. The discovery of pathogenic serotype AD hybrid strains in nature indicates that intervariety mating in C. neoformans occurs in the natural environment. However, little is known about the genetic consequences of hybridization in C. neoformans. Here, we analyzed a hybrid population of 163 progeny from a cross between strains of serotypes A (CDC15) and D (JEC20), using 114 codominant nuclear PCR–RFLP markers and 1 direct PCR marker. These markers were distributed on all 14 chromosomes of the sequenced strain JEC21 that was isogenic to one of the parents (JEC20) in our cross. Our analyses identified that of the 163 progeny, 5 were heterozygous at all 115 loci, 1 was completely homozygous and identical to one of the parents (CDC15), and the remai...
Genetic Diversity and Genomic Plasticity of Cryptococcus neoformans AD Hybrid Strains
G3 (Bethesda, Md.), 2012
Natural hybridization between two strains, varieties, or species is a common phenomenon in both plants and animals. Although hybridization may skew established gene pools, it generates population diversity efficiently and sometimes results in the emergence of newly adapted genotypes. Cryptococcus neoformans, which causes the most frequent opportunistic fungal infection in immunocompromised hosts, has three serotypes: A, D, and AD. Serotype-specific multilocus sequence typing and serotype-specific comparative genome hybridization were applied to investigate the genetic variability and genomic organization of C. neoformans serotype AD isolates. We confirm that C. neoformans serotype AD isolates are hybrids of serotype A and D strains. Compared with haploid strains, most AD hybrid isolates exhibit unique multilocus sequence typing genotypes, suggesting that multiple independent hybridization events punctuated the origin and evolutionary trajectory of AD hybrids. The MATa alleles from b...
Impact of Mating Type, Serotype, and Ploidy on the Virulence of Cryptococcus neoformans
Infection and Immunity, 2008
Hybridization with polyploidization is a significant biological force driving evolution. The effect of combining two distinct genomes in one organism on the virulence potential of pathogenic fungi is not clear. Cryptococcus neoformans , the most common cause of fungal infection of the central nervous system, has a bipolar mating system with a and α mating types and occurs as A (haploid), D (haploid), and AD hybrid (mostly diploid) serotypes. Diploid AD hybrids are derived either from a -α mating or from unisexual mating between haploid cells. The precise contributions of increased ploidy, the effect of hybridization between serotypes A and D, and the combination of mating types to the virulence potential of AD hybrids have remained elusive. By using in vitro and in vivo characterization of laboratory-constructed isogenic diploids and AD hybrids with all possible mating type combinations in defined genetic backgrounds, we found that higher ploidy has a minor negative effect on virule...