Association between fertility and molecular sub-type of global isolates of Cryptococcus gattii molecular type VGII

The basidiomycetous yeast Cryptococcus gattii, is a primary pathogen which causes disease in apparently healthy humans and a wide range of animals. Recently, an outbreak of cryptococcosis caused by a previously uncommon genotype of C. gattii, VGII, emerged on Vancouver Island, British Columbia, Canada. Two pathogenic sub-types of VGII (designated VGIIa and VGIIb) were identified among these isolates. All of the isolates proved to be mating type α and had exceptionally high sporulation capacity. The common subtype, VGIIa, was more virulent than VGIIb in mice, suggesting a linkage between subtype and fertility/ virulence. To test this hypothesis, we compared the fertility of 91 isolates from the Vancouver Island outbreak with that of 72 VGII isolates selected globally. Of all isolates, 69.94% were found to be fertile and exhibited clamp connections and basidiospores. The Vancouver isolates showed a high fertility rate of 84.2% as compared to only 29% of the 21 Australian isolates investigated. Mating type α strains were more fertile (72.79%) than mating type a (43.75%) (p < 0.022). Amongst the two subtypes of VGII a much higher proportion of VGIIa (91.7%) than VGIIb (33.3%) was fertile (p < 0.001). These results suggest that there is a clear correlation between the VGII subtypes of C. gattii and their mating/fertility. Further in vitro and in vivo investigations of more strains and congenic pairs are warranted.