Eukaryotic Cell doi:10.1128/EC.00097-08
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.
Isolates of Cryptococcus neoformans from infected animals reveal genetic exchange in unisexual, 
mating type populations
Tien Bui,
Xiaorong Lin,
Richard Malik,
Joseph Heitman,
and
Dee Carter*
Discipline of Microbiology, School of Molecular and Microbial Biosciences, University of Sydney, NSW 2006, Australia; Post Graduate Foundation of Veterinary Science and Faculty of Veterinary Science, University of Sydney, NSW 2006, Australia; Department of Molecular Genetics and Microbiology, Duke University Medical Center, Durham, NC 27710, USA
* To whom correspondence should be addressed. Email:
d.carter{at}mmb.usyd.edu.au.
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Abstract |
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Sexual reproduction and genetic exchange are important for the evolution of fungal pathogens and for producing potentially infective spores. Studies to determine whether sex occurs in the pathogenic yeast Cryptococcus neoformans var. grubii have produced enigmatic results, however: basidiospores are the most likely infective propagules and clinical isolates are fertile and genetically diverse, consistent with a sexual species, but almost all populations examined consist of a single mating type and have little evidence for genetic recombination. The choice of population is critical when looking for recombination, particularly when significant asexual propagation is likely and when latency may complicate assessing the origin of an isolate. We therefore selected isolates from infected animals living in the Sydney region, with the assumption that the relatively short life span and limited travel of the animal host would provide a very defined population. All isolates were mating type 
and were of molecular genotype VNI or VNII. Lack of linkage disequilibrium among loci suggested genetic exchange occurred within both genotype groups. Four diploid VNII isolates were found that produced filaments and basidia-like structures when cultured in proximity to an a mating-type strain. Recent studies suggest compatible - unions can occur in C. neoformans var. neoformans and in the sibling species Cryptococcus gattii. As a mating type strains of C. neoformans var. grubii have never been found in Australia, or in the VNII molecular type globally, this is evidence that - unisexual mating maintains sexual recombination and diversity in this pathogen and may produce infectious propagules.
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