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Identification of novel hybrids between Cryptococcus neoformans var. grubii VNI and Cryptococcus gattii VGII
Mojgan Aminnejad1, Mara Diaz, Michael Arabatzis
1Molecular Mycology Research Laboratory, Westmead, Australia.
Abstract:
Cryptococcus neoformans and Cryptococcus gattii are pathogenic yeasts causing meningoencephalitis in immunocompromised and immunocompetent hosts. The fungus is typically haploid, and sexual reproduction occurs normally between individuals with opposite mating types, α and a. C. neoformans var. grubii (serotype A) is comprised of molecular types VNI, VNII, and VNB, and C. neoformans var. neoformans (serotype D) contains the molecular type VNIV. Additionally, diploid or aneuploid AD hybrids (VNIII) have been reported. C. gattii contains the molecular types VGI, VGII, VGIII, and VGIV, which encompass both serotypes B and C. To identify possible hybrid strains, URA5-RFLP analysis was performed on 350 globally obtained clinical, environmental, and veterinary isolates. Four clinical isolates from cerebrospinal fluid showed combination patterns of C. neoformans var. grubii and C. gattii: Brazil (n = 2), Colombia (n = 1), and India (n = 1). These strains were monokaryotic and diploid or aneuploid. M13 PCR fingerprinting showed that they contained fragments of both proposed parental groups. Luminex IGS genotyping identified these isolates as hybrids with two different molecular type combinations: three VNI/VGII and one VNI/VGI. Blue color development on CGB agar was delayed in three isolates and absent in one. C. gattii-specific PCR confirmed the presence of C. gattii in the hybrids. CAP59 allele-specific PCR revealed that all the hybrids contained both serotype A and B alleles. Determination of mating-type allelic patterns by PCR revealed that the isolates were αA aB. This is the first study discovering novel natural hybrids between C. neoformans molecular type VNI and C. gattii molecular type VGII.
Insights
This study discovered novel natural hybrids between Cryptococcus neoformans and Cryptococcus gattii, identified in clinical samples. These hybrids exhibit characteristics of both parent species, expanding our understanding of fungal genetics and pathogenesis.
Area of Science:
- Mycology
- Medical Mycology
- Molecular Biology
Background:
- Cryptococcus neoformans and Cryptococcus gattii are significant fungal pathogens causing meningoencephalitis.
- These yeasts exist as haploid organisms with distinct mating types, and hybridization has been previously reported.
- Understanding the genetic diversity and hybrid formation is crucial for tracking fungal evolution and disease emergence.
Purpose of the Study:
- To identify and characterize novel natural hybrid strains between Cryptococcus neoformans and Cryptococcus gattii.
- To investigate the genetic makeup and molecular types of these potential hybrid isolates.
- To confirm the presence of genetic material from both parent species in the identified hybrids.
Main Methods:
- Screening of 350 clinical, environmental, and veterinary isolates using URA5-RFLP analysis.
- Characterization of hybrid candidates using M13 PCR fingerprinting, Luminex IGS genotyping, and species-specific PCR assays.
- Allele-specific PCR for CAP59 and mating-type determination by PCR were employed for detailed genetic analysis.
Main Results:
- Four clinical isolates from cerebrospinal fluid (Brazil, Colombia, India) displayed hybrid patterns of C. neoformans var. grubii and C. gattii.
- Genotyping identified three isolates as VNI/VGII hybrids and one as a VNI/VGI hybrid, all diploid or aneuploid.
- Hybrids confirmed the presence of C. gattii, both serotype A and B alleles, and possessed an αA aB mating type.
Conclusions:
- This study reports the first discovery of natural hybrids between Cryptococcus neoformans molecular type VNI and Cryptococcus gattii molecular type VGII.
- The identified hybrids possess a unique genetic combination, suggesting potential implications for virulence and antifungal resistance.
- Further research is warranted to understand the clinical significance and epidemiological impact of these novel hybrid strains.
