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Evidence of Recombination in Mixed-Mating-Type and -Only Populations of Cryptococcus gattii Sourced from Single Eucalyptus Tree Hollows

Faculty of Veterinary Science, University of Sydney,¹ School of Molecular and Microbial Biosciences, University of Sydney, Sydney, Australia²

Received 15 January 2008/ Accepted 6 February 2008

Disease caused by the pathogenic yeast Cryptococcus gattii begins with the inhalation of an infectious propagule. As C. gattii is heavily encapsulated, this propagule is most likely to be a basidiospore. However, most C. gattii strains are infertile in laboratory crosses, and population studies indicate that recombination and dispersal are very restricted. In addition, strains of the mating type predominate, which would not be expected in a mating population. C. gattii comprises four genetically distinct molecular genotypes, designated VGI to VGIV. C. gattii molecular type VGI has a strong association with Eucalyptus camaldulensis and can be found in high numbers in E. camaldulensis hollows. Previous work on isolates obtained from E. camaldulensis suggested that environmental populations of C. gattii are highly fragmented, have limited ability to disperse, and are confined to individual tree hollows. In the current study, we examined large numbers of isolates from three separate hollows for evidence of recombination. In two hollows, the and a mating types were present in approximately equal numbers. The third hollow had cells only and was from a region where a isolates have never been found. Statistical analysis of multilocus genotypes revealed recombining subpopulations in the three Eucalyptus hollows. Recombination was equally present in the -a and -only populations. This is consistent with recent studies that have found evidence suggestive of - mating in C. gattii and Cryptococcus neoformans and raises the possibility this may be a widespread phenomenon, allowing these fungi to recombine despite a paucity of a mating partners.

Published ahead of print on 15 February 2008.