Biogenesis, germination, and pathogenesis of Cryptococcus spores

Abstract

SUMMARYSpores are primary infectious propagules for the majority of human fungal pathogens; however, relatively little is known about their fundamental biology. One strategy to address this deficiency has been to develop the basidiospores of Cryptococcus into a model for pathogenic spore biology. Here, we provide an update on the state of the field with a comprehensive review of the data generated from the study of Cryptococcus basidiospores from their formation (sporulation) and differentiation (germination) to their roles in pathogenesis. Importantly, we provide support for the presence of basidiospores in nature, define the key characteristics that distinguish basidiospores from yeast cells, and clarify their likely roles as infectious particles. This review is intended to demonstrate the importance of basidiospores in the field of Cryptococcus research and provide a solid foundation from which researchers who wish to study sexual spores in any fungal system can launch their studies.

Keywords: Cryptococcus; basidiospore; fungal pathogenesis; germination; mycology; sexual development; sporulation.

Fig 1

Representative scanning electron microscopy (SEM) images of Cryptococcus undergoing sexual development, resulting in sporulation and the formation of long spore chains (false colored in brown). (SEM images courtesy of Eddie Dominguez, used with permission.)

Fig 2

Representative SEM images of Cryptococcus spores at different stages of germination (left, ungerminated; middle, partially germinated; right, fully germinated and budding). False coloring used to display original spore coat (brown) and newly formed yeast surface (gold). (SEM images courtesy of Eddie Dominguez, used with permission.)

Fig 3

SEM image of a cluster of six Cryptococcus spores (brown) undergoing internalization by a macrophage (blue-gray). (SEM images courtesy of Eddie Dominguez, used with permission.)

Fig 4

Model of key aspects of Cryptococcus spore biology: biogenesis of spores during sexual development (sporulation), transition from quiescent spore to replicating yeast (germination), and infection and disease in a mammalian host (pathogenesis).