Conservation of intracellular pathogenic strategy among distantly related cryptococcal species

The genus Cryptococcus includes several species pathogenic for humans. Until recently, the two major pathogenic species were recognized to be Cryptococcus neoformans and Cryptococcus gattii. We compared the interaction of murine macrophages with three C. gattii species complex strains (WM179, R265, and WM161, representing molecular types VGI, VGIIa, and VGIII, respectively) and one C. neoformans species complex strain (H99, molecular type VNI) to ascertain similarities and differences in the yeast intracellular pathogenic strategy. The parameters analyzed included nonlytic exocytosis frequency, phagolysosomal pH, intracellular capsular growth, phagolysosomal membrane permeabilization, and macrophage transcriptional response, assessed using time-lapse microscopy, fluorescence microscopy, flow cytometry, and gene expression microarray analysis. The most striking result was that the intracellular pathogenic strategies of C. neoformans and C. gattii species complex strains were qualitatively similar, despite the species having separated an estimated 100 million years ago. Macrophages exhibited a leaky phagolysosomal membrane phenotype and nonlytic exocytosis when infected with either C. gattii or C. neoformans. Conservation of the intracellular strategy among species that separated long ago suggests that it is ancient and possibly maintained by similar selection pressures through eons.