Lineages Derived from Cryptococcus neoformans Type Strain H99 Support a Link between the Capacity to Be Pleomorphic and Virulence

The pathogenic yeast Cryptococcus neoformans causes nearly 200,000 deaths annually in immunocompromised individuals. Cryptococcus cells can undergo substantial morphological change during mammalian infection, including increased capsule and cell size, the release of shed capsule, and the production of titan (>10 mu m), micro (<2 mu m)-, and irregular cells. We examined phenotypic variation under conditions designed to simulate in vivo stress in a collection of nine lineages derived from the C. neoformans type strain H99. These lineages are highly genetically similar but have a range of virulence levels. Strains from hypervirulent lineages had a larger average capsule size, greater variation in cell size, and an increased production of microcells and shed capsule. We tested whether disruption of SGF29, which encodes a component of the SAGA histone acetylation complex that has previously been implicated in the hypervirulence of some lineages, also has a role in the production of morphological variants. Deletion of SGF29 in a lineage with intermediate virulence substantially increased its production of microcells and released capsule, consistent with a switch to hypervirulence. We further examined SGF29 in a set of 52 clinical isolates and found loss-of-function mutations were significantly correlated with patient death. Expansion of a TA repeat in the second intron of SGF29 was positively correlated with cell and capsule size, suggesting it also affects Sgf29 function. This study extends the evidence for a link between pleomorphism and virulence in Cryptococcus, with a likely role for epigenetic mechanisms mediated by SAGA-induced histone acetylation. IMPORTANCE Cryptococcosis is a devastating cause of death and disease worldwide. During infection, Cryptococcus cells can undergo substantial changes to their size and shape. In this study, we used a collection of C. neoformans strains that are highly genetically similar but possess differing levels of virulence to investigate how morphological variation aligns with virulence. We found hypervirulent strains on average had larger capsules and greater variation in cell size and produced more microcells and shed capsule. These hypervirulent strains possessed a mutation in SGF29, which encodes a component of the SAGA complex involved in epigenetic regulation. Analysis of the SGF29 gene in a set of clinical isolates found strains with loss-of-function mutations were associated with higher patient death rates. The capacity to vary appears to be linked with virulence in Cryptococcus, and this can occur in the absence of genetic variation via epigenetic mechanisms. Cryptococcosis is a devastating cause of death and disease worldwide. During infection, Cryptococcus cells can undergo substantial changes to their size and shape.

Automated summary

Cryptococcosis is a devastating cause of death and disease worldwide. During infection, Cryptococcus cells can undergo substantial changes to their size and shape. In this study, researchers found that hypervirulent strains of Cryptococcus had larger capsules, greater variation in cell size, and produced more microcells and shed capsule. These hypervirulent strains had a mutation in the SGF29 gene, which encodes a component of the SAGA complex involved in epigenetic regulation. Analysis of clinical isolates also showed a correlation between loss-of-function mutations in SGF29 and higher patient death rates. The study suggests that the ability to undergo morphological variation is linked to virulence in Cryptococcus, and this can occur through epigenetic mechanisms.