Expanding fungal pathogenesis: Cryptococcus breaks out of the opportunistic box

Key Points

  • Cryptococcus neoformans is generally considered to be an opportunistic pathogen because of its tendency to infect immunocompromised individuals. However, this view has been challenged by recent discoveries of specialized interactions between the fungus and its mammalian hosts, and by the emergence of the related species Cryptococcus gattii as a primary pathogen of immunocompetent populations.

  • Methods have been developed to separate the yeast cells (4–10 μm) from the spores (1–2 μm in diameter) that result from sexual development and meiosis in C. neoformans. The spores are infectious, as has long been suspected, and they are readily phagocytosed by macrophages in the absence of an opsonin, whereas yeast cells require prior opsonization.

  • C. neoformans and C. gattii disseminate from the lung and cross the blood–brain barrier (BBB) to cause meningoencephalitis. The fungal cells cross the BBB directly by transcytosis through endothelial cells lining vessels in the brain, and by a 'Trojan Horse' strategy that involves transport in phagocytic cells.

  • Intracellular cryptococcal cells residing in phagosomes can escape their phagocytic host cells by expulsion and by cell-to-cell transfer between macrophages. Cycles of actin polymerization (actin 'flashes') seem to form transient cages around phagosomes, potentially providing a barrier to expulsion.

  • C. gattii has emerged as a pathogen of immunocompetent humans and animals in western North America. The associated C. gattii strains appear to have a high intracellular proliferation rate in macrophages, and this is correlated with their virulence; they also trigger a reduced protective inflammatory response compared with the response triggered by a representative C. neoformans strain.

  • Giant cells (up to 100 μm) account for 20% of the cryptococcal burden during lung infection. These cells are polyploid and resistant to phagocytosis.

  • Studies with fresh isolates of C. neoformans from patients with AIDS revealed that mixed infections, as well as changes in ploidy resulting from endoreplication, are more common during cryptococcosis than previously thought. In addition, clinical isolates and strains that display antifungal-drug resistance can harbour disomic chromosomes.

Abstract

Cryptococcus neoformans is generally considered to be an opportunistic fungal pathogen because of its tendency to infect immunocompromised individuals, particularly those infected with HIV. However, this view has been challenged by the recent discovery of specialized interactions between the fungus and its mammalian hosts, and by the emergence of the related species Cryptococcus gattii as a primary pathogen of immunocompetent populations. In this Review, we highlight features of cryptococcal pathogens that reveal their adaptation to the mammalian environment. These features include not only remarkably sophisticated interactions with phagocytic cells to promote intracellular survival, dissemination to the central nervous system and escape, but also surprising morphological and genomic adaptations such as the formation of polyploid giant cells in the lung.

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Figure 1: Morphologically distinct cell types contribute to virulence in Cryptococcus neoformans.
Figure 2: Interactions of fungal cells with phagocytic cells, and fungal dissemination through the blood–brain barrier.
Figure 3: Giant cell formation and variation in genome copy number.

References

  1. 1

    Brizendine, K. D. & Pappas, P. G. Cryptococcal meningitis: Current approaches to management in patients with and without AIDS. Curr. Infect. Dis. Rep. 12, 299–305 (2010).

    Article  PubMed  Google Scholar 

  2. 2

    Park, B. J. et al. Estimation of the current global burden of cryptococcal meningitis among persons living with HIV/AIDS. AIDS 23, 525–30 (2009). This study provides the first global view of the burden of cryptococcosis and reveals that there are 1 million cases per year, resulting in 625,000 deaths. The highest burden is in sub-Saharan Africa.

    Article  PubMed  Google Scholar 

  3. 3

    Bartlett, K. H., Kidd, S. E. & Kronstad, J. W. The emergence of Cryptococcus gattii in British Columbia and the Pacific Northwest. Curr. Infect. Dis. Rep. 10, 58–65 (2008).

    Article  PubMed  Google Scholar 

  4. 4

    Byrnes, E. J. 3rd et al. Molecular evidence that the range of the Vancouver Island outbreak of Cryptococcus gattii infection has expanded into the Pacific Northwest in the United States. J. Infect. Dis. 199, 1081–1086 (2009).

    Article  PubMed  PubMed Central  Google Scholar 

  5. 5

    Byrnes, E. J. 3rd et al. Emergence and pathogenicity of highly virulent Cryptococcus gattii genotypes in the northwest United States. PLoS Pathog. 6, e1000850 (2010).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  6. 6

    Datta, K. et al. Spread of Cryptococcus gattii into Pacific Northwest region of the United States. Emerg. Infect. Dis. 15, 1185–1191 (2009).

    Article  PubMed  PubMed Central  Google Scholar 

  7. 7

    Galanis, E. & Macdougall, L. Epidemiology of Cryptococcus gattii, British Columbia, Canada, 1999–2007. Emerg. Infect. Dis. 16, 251–257 (2010).

    Article  PubMed  PubMed Central  Google Scholar 

  8. 8

    Kwon-Chung, K. J., Boekhout, T., Fell, J. W. & Diaz, M. Proposal to conserve the name Cryptococcus gattii against C. hondurianus and C. bacillisporus (Basidiomycota, Hymenomycetes, Tremellomycetidae). Taxon 51, 804–806 (2002).

    Article  Google Scholar 

  9. 9

    Mitchell, T. G. & Perfect, J. R. Cryptococcosis in the era of AIDS—100 years after the discovery of Cryptococcus neoformans. Clin. Microbiol. Rev. 8, 515–548 (1995).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  10. 10

    Sorrell, T. C. Cryptococcus neoformans variety gattii. Med. Mycol. 39, 155–168 (2001).

    Article  CAS  PubMed  Google Scholar 

  11. 11

    Casadevall, A., Nosanchuk, J. D., Williamson, P. & Rodrigues, M. L. Vesicular transport across the fungal cell wall. Trends Microbiol. 17, 158–162 (2009).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  12. 12

    Casadevall, A. & Pirofski, L. A. The damage-response framework of microbial pathogenesis. Nature Rev. Microbiol. 1, 17–24 (2003).

    Article  CAS  Google Scholar 

  13. 13

    Idnurm, A. et al. Deciphering the model pathogenic fungus Cryptococcus neoformans. Nature Rev. Microbiol. 3, 753–764 (2005).

    Article  CAS  Google Scholar 

  14. 14

    Jung, W. H. & Kronstad, J. W. Iron and fungal pathogenesis: a case study with Cryptococcus neoformans. Cell. Microbiol. 10, 277–284 (2008).

    Article  CAS  PubMed  Google Scholar 

  15. 15

    Doering, T. L. How sweet it is! Cell wall biogenesis and polysaccharide capsule formation in Cryptococcus neoformans. Annu. Rev. Microbiol. 63, 223–247 (2009).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  16. 16

    Kozubowski, L., Lee, S. C. & Heitman, J. Signalling pathways in the pathogenesis of Cryptococcus. Cell. Microbiol. 11, 370–380 (2009).

    Article  CAS  PubMed  Google Scholar 

  17. 17

    Lin, X. Cryptococcus neoformans: morphogenesis, infection, and evolution. Infect. Genet. Evol. 9, 401–416 (2009).

    Article  CAS  PubMed  Google Scholar 

  18. 18

    Ma, H. & May, R. C. Virulence in Cryptococcus species. Adv. Appl. Microbiol. 67, 131–190 (2009).

    Article  CAS  PubMed  Google Scholar 

  19. 19

    Zaragoza, O. et al. The capsule of the fungal pathogen Cryptococcus neoformans. Adv. Appl. Microbiol. 68, 133–216 (2009).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  20. 20

    Voelz, K. & May, R. C. Cryptococcal interactions with the host immune system. Eukaryot. Cell 9, 835–846 (2010).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  21. 21

    Casadevall, A. & Perfect, J. R. Cryptococcus neoformans (American Society for Microbiology Press, Washington DC, 1998).

    Google Scholar 

  22. 22

    Heitman, J., Kozel, T. R., Kwon-Chung, K. J., Perfect, J. R. & Casadevall, A. (eds) Cryptococcus: From Human Pathogen to Model Yeast (American Society for Microbiology Press, Washington DC, 2010).

    Google Scholar 

  23. 23

    Lin, X, Hull, C. M. & Heitman J. Sexual reproduction between partners of the same mating type in Cryptococcus neoformans. Nature 434, 1017–1021 (2005).

    Article  CAS  Google Scholar 

  24. 24

    Botts, M. R., Giles, S. S., Gates, M. A., Kozel, T. R. & Hull, C. M. Isolation and characterization of Cryptococcus neoformans spores reveal a critical role for capsule biosynthesis genes in spore biogenesis. Eukaryot. Cell 8, 595–605 (2009).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  25. 25

    Xue, C., Tada, Y., Dong, X. & Heitman, J. The human fungal pathogen Cryptococcus can complete its sexual cycle during a pathogenic association with plants. Cell Host Microbe 1, 263–273 (2007).

    Article  CAS  PubMed  Google Scholar 

  26. 26

    Velagapudi, R., Hsueh, Y. P., Geunes-Boyer, S., Wright, J. R. & Heitman, J. Spores as infectious propagules of Cryptococcus neoformans. Infect. Immun. 77, 4345–4355 (2009). This article and reference 24 describe the development of methods to isolate and characterize cryptococcal spores.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  27. 27

    Vartivarian, S. E. et al. Regulation of cryptococcal capsular polysaccharide by iron. J. Infect. Dis. 167, 186–190 (1993).

    Article  CAS  PubMed  Google Scholar 

  28. 28

    Giles, S. S., Dagenais, T. R., Botts, M. R., Keller, N. P. & Hull, C. M. Elucidating the pathogenesis of spores from the human fungal pathogen Cryptococcus neoformans. Infect. Immun. 77, 3491–3500 (2009). This article and reference 26 provide evidence that cryptococcal spores are infectious agents, and analyse the interactions of spores with phagocytic cells. This article also describes initial studies of spore surface molecules such as β-(1,3)-glucan, and of macrophage receptors such as dectin 1.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  29. 29

    Feldmesser, M., Kress, Y., Novikoff, P. & Casadevall, A. Cryptococcus neoformans is a facultative intracellular pathogen in murine pulmonary infection. Infect. Immun. 68, 4225–4237 (2000).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  30. 30

    Botts, M. R. & Hull, C. M. Dueling in the lung: how Cryptococcus spores race the host for survival. Curr. Opin. Microbiol. 13, 437–442 (2010).

    Article  PubMed  PubMed Central  Google Scholar 

  31. 31

    Chang, Y. C. et al. Cryptococcal yeast cells invade the central nervous system via transcellular penetration of the blood-brain barrier. Infect. Immun. 72, 4985–4995 (2004).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  32. 32

    Shea, J. M., Kechichian, T. B., Luberto, C. & Del Poeta, M. The cryptococcal enzyme inositol phosphosphingolipid-phospholipase C confers resistance to the antifungal effects of macrophages and promotes fungal dissemination to the central nervous system. Infect. Immun. 74, 5977–5988 (2006).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  33. 33

    Kechichian, T. B., Shea, J. & Del Poeta, M. Depletion of alveolar macrophages decreases the dissemination of a glucosylceramide-deficient mutant of Cryptococcus neoformans in immunodeficient mice. Infect. Immun. 75, 4792–4798 (2007).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  34. 34

    Charlier, C. et al. Capsule structure changes associated with Cryptococcus neoformans crossing of the blood-brain barrier. Am. J. Pathol. 166, 421–432 (2005).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  35. 35

    Charlier, C. et al. Evidence of a role for monocytes in dissemination and brain invasion by Cryptococcus neoformans. Infect. Immun. 77, 120–127 (2009). Convincing evidence is presented to support the Trojan Horse mechanism for C. neoformans crossing the blood–brain barrier, and for a general role for monocytes in tissue seeding.

    Article  CAS  PubMed  Google Scholar 

  36. 36

    Shi, M. et al. Real-time imaging of trapping and urease-dependent transmigration of Cryptococcus neoformans in mouse brain. J. Clin. Invest. 120, 1683–1693 (2010). IVM demonstrates that C. neoformans cells are mechanically trapped in mouse brain capillaries and actively transmigrate to the brain parenchyma.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  37. 37

    Wilson, R. A. & Talbot, N. J. Under pressure: investigating the biology of plant infection by Magnaporthe oryzae. Nature Rev. Microbiol. 7, 185–195 (2009).

    Article  CAS  Google Scholar 

  38. 38

    Olszewski, M. A. et al. Urease expression by Cryptococcus neoformans promotes microvascular sequestration, thereby enhancing central nervous system invasion. Am. J. Pathol. 164, 1761–1771 (2004).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  39. 39

    Lortholary, O. et al. Fungemia during murine cryptococcosis sheds some light on pathophysiology. Med. Mycol. 37, 169–174 (1999).

    CAS  PubMed  Google Scholar 

  40. 40

    Chretien, F. et al. Pathogenesis of cerebral Cryptococcus neoformans infection after fungemia. J. Infect. Dis. 186, 522–530 (2002).

    Article  PubMed  Google Scholar 

  41. 41

    Alvarez, M. & Casadevall, A. Phagosome extrusion and host-cell survival after Cryptococcus neoformans phagocytosis by macrophages. Curr. Biol. 16, 2161–2165 (2006).

    Article  CAS  PubMed  Google Scholar 

  42. 42

    Levitz, S. M. et al. Cryptococcus neoformans resides in an acidic phagolysosome of human macrophages. Infect. Immun. 67, 885–890 (1999).

    CAS  PubMed  PubMed Central  Google Scholar 

  43. 43

    Tucker, S. C. & Casadevall, A. Replication of Cryptococcus neoformans in macrophages is accompanied by phagosomal permeabilization and accumulation of vesicles containing polysaccharide in the cytoplasm. Proc. Natl Acad. Sci. USA 99, 3165–3170 (2002).

    Article  CAS  PubMed  Google Scholar 

  44. 44

    Alvarez, M. & Casadevall, A. Cell-to-cell spread and massive vacuole formation after Cryptococcus neoformans infection of murine macrophages. BMC Immunol. 8, 16 (2007).

    PubMed  PubMed Central  Google Scholar 

  45. 45

    Ma, H., Croudace, J. E., Lammas, D. A. & May, R. C. Expulsion of live pathogenic yeast by macrophages. Curr. Biol. 16, 2156–2160 (2006).

    Article  CAS  PubMed  Google Scholar 

  46. 46

    Ma, H., Croudace, J. E., Lammas, D. A. & May, R. C. Direct cell-to-cell spread of a pathogenic yeast. BMC Immunol. 8, 15 (2007).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  47. 47

    Johnston, S. A. & May, R. C. The human fungal pathogen Cryptococcus neoformans escapes macrophages by a phagosome emptying mechanism that is inhibited by Arp2/3 complex-mediated actin polymerisation. PLoS Pathog. 6, e1001041 (2010). This report finds evidence of repeated cycles of actin polymerization in phagosomes containing cryptococcal cells, producing cages that may temporarily inhibit expulsion of the fungal cells.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  48. 48

    Yam, P. T. & Theriot, J. A. Repeated cycles of rapid actin assembly and disassembly on epithelial cell phagosomes. Mol. Biol. Cell 15, 5647–5658 (2004).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  49. 49

    Ma, H. et al. The fatal fungal outbreak on Vancouver Island is characterized by enhanced intracellular parasitism driven by mitochondrial regulation. Proc. Natl Acad. Sci. USA 106, 12980–12985 (2009). This paper demonstrates that isolates from the British Columbia outbreak have an increased capacity to proliferate in macrophages, and show an altered mitochondrial morphology after phagocytosis. These results suggest that intracellular parasitic capability is an important component of the outbreak.

    Article  CAS  Google Scholar 

  50. 50

    Cheng, P. Y., Sham, A. & Kronstad, J. W. Cryptococcus gattii isolates from the British Columbia cryptococcosis outbreak induce less protective inflammation in a murine model of infection than Cryptococcus neoformans. Infect. Immun. 77, 4284–4294 (2009). The first examination of immune response to the outbreak isolates demonstrates a reduced production of pro-inflammatory cytokines and a decrease in neutrophil infiltration in the lungs of mice infected with C. gattii , when compared with levels in mice infected with C. neoformans.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  51. 51

    Cruickshank, J. G., Cavill, R. & Jelbert, M. Cryptococcus neoformans of unusual morphology. Appl. Microbiol. 25, 309–312 (1973).

    CAS  PubMed  PubMed Central  Google Scholar 

  52. 52

    Love, G. L., Boyd, G. D. & Greer, D. L. Large Cryptococcus neoformans isolated from brain abscess. J. Clin. Microbiol. 22, 1068–1070 (1985).

    CAS  PubMed  PubMed Central  Google Scholar 

  53. 53

    Sia, R. A., Lengeler, K. B. & Heitman, J. Diploid strains of the pathogenic basidiomycete Cryptococcus neoformans are thermally dimorphic. Fungal Genet. Biol. 29, 153–163 (2000).

    Article  CAS  PubMed  Google Scholar 

  54. 54

    Zaragoza, O., Fries, B. C. & Casadevall, A. Induction of capsule growth in Cryptococcus neoformans by mammalian serum and CO2 . Infect. Immun. 71, 6155–6164 (2003).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  55. 55

    Zaragoza, O. et al. Fungal cell gigantism during mammalian infection. PLoS Pathog. 6, e1000945 (2010).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  56. 56

    Nielsen, K. et al. Cryptococcus neoformans α strains preferentially disseminate to the central nervous system during coinfection. Infect. Immun. 73, 4922–4933 (2005).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  57. 57

    Hsueh, Y. P. & Heitman, J. Orchestration of sexual reproduction and virulence by the fungal mating-type locus. Curr. Opin. Microbiol. 11, 517–524 (2008).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  58. 58

    Okagaki, L. H. et al. Cryptococcal cell morphology affects host cell interactions and pathogenicity. PLoS Pathog. 6, e1000953 (2010). Along with reference 55, this study provides the first detailed characterization of giant cells and reveals their resistance to phagocytosis and their polyploid genome content.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  59. 59

    Feldmesser, M., Kress, Y. & Casadevall A. Dynamic changes in the morphology of Cryptococcus neoformans during murine pulmonary infection. Microbiology 147, 2355–2365 (2001).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  60. 60

    D'Souza, C. A. et al. Cyclic AMP-dependent protein kinase controls virulence of the fungal pathogen Cryptococcus neoformans. Mol. Cell. Biol. 21, 3179–3191 (2001).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  61. 61

    Klein, B. S. & Tebbets, B. Dimorphism and virulence in fungi. Curr. Opin. Microbiol. 10, 314–319 (2007).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  62. 62

    Desnos-Ollivier, M. et al. Mixed infections and in vivo evolution in the human fungal pathogen Cryptococcus neoformans. mBio 1, e00091–10 (2010). An intriguing survey of fresh isolates demonstrates that mixed infections with strains of different mating types, serotypes and genotypes are present in approximately 20% of patients. This study also reveals that transitions between haploid and diploid states can occur during infection.

    Article  PubMed  PubMed Central  Google Scholar 

  63. 63

    Torres, E. M. et al. Effects of aneuploidy on cellular physiology and cell division in haploid yeast. Science 317, 916–924 (2007).

    Article  CAS  PubMed  Google Scholar 

  64. 64

    Galitski, T., Saldanha, A. J., Styles, C. A., Lander, E. S. & Fink, G. R. Ploidy regulation of gene expression. Science 285, 251–254 (1999).

    Article  CAS  PubMed  Google Scholar 

  65. 65

    Selmecki, A., Forche, A. & Berman, J. Genomic plasticity of the human fungal pathogen Candida albicans. Eukaryot. Cell 9, 991–1008 (2010).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  66. 66

    Fries, B. C., Chen, F., Currie, B. P. & Casadevall, A. Karyotype instability in Cryptococcus neoformans infection. J. Clin. Microbiol. 34, 1531–1534 (1996).

    CAS  PubMed  PubMed Central  Google Scholar 

  67. 67

    Loftus, B. J. et al. The genome of the basidiomycetous yeast and human pathogen Cryptococcus neoformans. Science 307, 1321–1324 (2005).

    Article  PubMed  PubMed Central  Google Scholar 

  68. 68

    Kavanaugh, L. A., Fraser, J. A. & Dietrich, F. S. Recent evolution of the human pathogen Cryptococcus neoformans by intervarietal transfer of a 14-gene fragment. Mol. Biol. Evol. 23, 1879–1890 (2006).

    Article  CAS  PubMed  Google Scholar 

  69. 69

    D'Souza, C. A. et al. Genome variation in Cryptococcus gattii, an emerging pathogen of immunocompetent hosts. mBio (in the press). This paper reports the genome sequences of strains representing the VGI and VGII genotypes of C. gattii , as well as comparative genome hybridization experiments to examine variation in avirulent, fluconazole-resistant and outbreak isolates.

  70. 70

    Hu, G. et al. Comparative hybridization reveals extensive genome variation in the AIDS-associated pathogen Cryptococcus neoformans. Genome Biol. 9, R41 (2008). The genome sequences of serotype A and serotype D strains are used in comparative studies to characterize genomic variability in strains of different molecular subtypes and in serotype AD hybrid strains. This analysis provides the first demonstration of disomy in clinical isolates of serotype A, the serotype that causes the majority of infections in patients with AIDS.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  71. 71

    Sionov, E., Lee, H., Chang, Y. C. & Kwon-Chung, K. J. Cryptococcus neoformans overcomes stress of azole drugs by formation of disomy in specific multiple chromosomes. PLoS Pathog. 6, e1000848 (2010). This study reveals that extensive disomy is associated with drug resistance and that chromosomes encoding the target of fluconazole inhibition (Erg11) or a drug efflux pump (Afr1) have elevated copy number in resistant isolates.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  72. 72

    Varma, A. & Kwon-Chung, K. J. Heteroresistance of Cryptococcus gattii to fluconazole. Antimicrob. Agents Chemother. 54, 2303–2311 (2010).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  73. 73

    Guerrero, A., Jain, N., Wang, X. & Fries, B. C. Cryptococcus neoformans variants generated by phenotypic switching differ in virulence through effects on macrophage activation. Infect. Immun. 78, 1049–1057 (2010).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  74. 74

    Lin, X. et al. Diploids in the Cryptococcus neoformans serotype A population homozygous for the α mating type originate via unisexual mating. PLoS Pathog. 5, e1000283 (2009).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  75. 75

    Rancati, G. et al. Aneuploidy underlies rapid adaptive evolution of yeast cells deprived of a conserved cytokinesis motor. Cell 135, 879–893 (2008).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  76. 76

    Duncan, A. W. et al. The ploidy conveyor of mature hepatocytes as a source of genetic variation. Nature 467, 707–710 (2010).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  77. 77

    Liu, O. W. et al. Systematic genetic analysis of virulence in the human fungal pathogen Cryptococcus neoformans. Cell 135, 174–188 (2008).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  78. 78

    CDC. Emergence of Cryptococcus gattii — Pacific Northwest, 2004–2010. MMWR 59, 865–868 (2010).

  79. 79

    Fraser, J. A. et al. Same-sex mating and the origin of the Vancouver Island Cryptococcus gattii outbreak. Nature 437, 1360–1364 (2005).

    Article  CAS  Google Scholar 

  80. 80

    Eisenman, H. C., Frases, S., Nicola, A. M., Rodrigues, M. L. & Casadevall, A. Vesicle-associated melanization in Cryptococcus neoformans. Microbiology 155, 3860–3867 (2009).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  81. 81

    Rodrigues, M. L. et al. Vesicular polysaccharide export in Cryptococcus neoformans is a eukaryotic solution to the problem of fungal trans-cell wall transport. Eukaryot. Cell 6, 48–59 (2007).

    Article  CAS  PubMed  Google Scholar 

  82. 82

    Rodrigues, M. L. et al. Extracellular vesicles produced by Cryptococcus neoformans contain protein components associated with virulence. Eukaryot. Cell 7, 58–67 (2008).

    Article  CAS  PubMed  Google Scholar 

  83. 83

    Yoneda, A. & Doering, T. L. A eukaryotic capsular polysaccharide is synthesized intracellularly and secreted via exocytosis. Mol. Biol. Cell 17, 5131–5140 (2006).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  84. 84

    Yoneda, A. & Doering, T. L. An unusual organelle in Cryptococcus neoformans links luminal pH and capsule biosynthesis. Fungal Genet. Biol. 46, 682–687 (2009).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  85. 85

    Hu, G. et al. Transcriptional regulation by protein kinase A in Cryptococcus neoformans. PLoS Pathog. 3, e42 (2007).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  86. 86

    Panepinto, J. et al. Sec6-dependent sorting of fungal extracellular exosomes and laccase of Cryptococcus neoformans. Mol. Microbiol. 71, 1165–1176 (2009).

    Article  CAS  PubMed  Google Scholar 

  87. 87

    Oliveira, D. L. et al. Extracellular vesicles from Cryptococcus neoformans modulate macrophage functions. Infect. Immun. 78, 1601–1609 (2010).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  88. 88

    Levitz, S. M. & Specht, C. A. The molecular basis for the immunogenicity of Cryptococcus neoformans mannoproteins. FEMS Yeast Res. 6, 513–524 (2006).

    Article  CAS  PubMed  Google Scholar 

  89. 89

    Nosanchuk, J. D. & Casadevall, A. Impact of melanin on microbial virulence and clinical resistance to antimicrobial compounds. Antimicrob. Agents Chemother. 50, 3519–3528 (2006).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  90. 90

    Panepinto, J. C. & Williamson, P. R. Intersection of fungal fitness and virulence in Cryptococcus neoformans. FEMS Yeast Res. 6, 489–498 (2006).

    Article  CAS  PubMed  Google Scholar 

  91. 91

    Zhu, X. & Williamson, P. R. Role of laccase in the biology and virulence of Cryptococcus neoformans. FEMS Yeast Res. 5, 1–10 (2004).

    Article  CAS  PubMed  Google Scholar 

  92. 92

    Perfect, J. R. Cryptococcus neoformans: the yeast that likes it hot. FEMS Yeast Res. 6, 463–468 (2006).

    Article  CAS  PubMed  Google Scholar 

  93. 93

    Brown, S. M., Campbell, L. T. & Lodge, J. K. Cryptococcus neoformans, a fungus under stress. Curr. Opin. Microbiol. 10, 320–325 (2007).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  94. 94

    Siafakas, A. R. et al. Cell wall-linked cryptococcal phospholipase B1 is a source of secreted enzyme and a determinant of cell wall integrity. J. Biol. Chem. 282, 37508–37514 (2007).

    Article  CAS  PubMed  Google Scholar 

  95. 95

    Cox, G. M., Mukherjee, J., Cole, G. T., Casadevall, A. & Perfect, J. R. Urease as a virulence factor in experimental cryptococcosis. Infect. Immun. 68, 443–448 (2000).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  96. 96

    de Jesús-Berríos, M. et al. Enzymes that counteract nitrosative stress promote fungal virulence. Curr. Biol. 13, 1963–1968 (2003).

    Article  CAS  PubMed  Google Scholar 

  97. 97

    Cox, G. M. et al. Superoxide dismutase influences the virulence of Cryptococcus neoformans by affecting growth within macrophages. Infect. Immun. 71, 173–180 (2003).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  98. 98

    Gerik, K. J., Bhimireddy, S. R., Ryerse, J. S., Specht, C. A. & Lodge, J. K. PKC1 is essential for protection against both oxidative and nitrosative stresses, cell integrity, and normal manifestation of virulence factors in the pathogenic fungus Cryptococcus neoformans. Eukaryot. Cell 7, 1685–1698 (2008).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  99. 99

    Hu, G. et al. PI3K signaling of autophagy is required for starvation tolerance and virulence of Cryptococcus neoformans. J. Clin. Invest. 118, 1186–1197 (2008).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  100. 100

    Rhome, R. & Del Poeta, M. Lipid signaling in pathogenic fungi. Annu. Rev. Microbiol. 63, 119–131 (2009).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  101. 101

    Bien, C. M. & Espenshade, P. J. Sterol regulatory element binding proteins in fungi: hypoxic transcription factors linked to pathogenesis. Eukaryot. Cell 9, 352–359 (2010).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  102. 102

    Fan, W., Kraus, P. R., Boily, M. J. & Heitman, J. Cryptococcus neoformans gene expression during murine macrophage infection. Eukaryot. Cell 4, 1420–1433 (2005).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  103. 103

    Hu, G., Cheng, P.-Y., Sham, A., Perfect, J. R. & Kronstad, J. W. Metabolic adaptation in Cryptococcus neoformans during early murine pulmonary infection. Mol. Microbiol. 69, 1456–1475 (2008).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  104. 104

    Lin, X. & Heitman, J. The biology of the Cryptococcus neoformans species complex. Annu. Rev. Microbiol. 60, 69–105 (2006).

    Article  CAS  PubMed  Google Scholar 

  105. 105

    O'Meara, T. R. et al. Interaction of Cryptococcus neoformans Rim101 and protein kinase A regulates capsule. PLoS Pathog. 6, e1000776 (2010).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  106. 106

    Jung, W. H., Sham, A., White, R. & Kronstad, J. W. Iron regulation of the major virulence factors in the AIDS-associated pathogen Cryptococcus neoformans. PLoS Biol. 4, e410 (2006).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

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Acknowledgements

We gratefully acknowledge support from the National Institute of Allergy and Infectious Diseases, US National Institutes of Health (RO1 AI053721) and the Canadian Institutes of Health Research. J.W.K. is a Burroughs Wellcome Fund Scholar in molecular pathogenic mycology.

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Glossary

Meningoencephalitis

A combination of infection and inflammation of the meninges (membranes surrounding the central nervous system) and the brain.

Capsule

A polysaccharide layer that surrounds cryptococcal cells and is composed of glucuronoxylomannan and galactoxylomannan.

Melanin

A brown or black polymer that is deposited in the fungal cell wall and results in part from the catalytic activity of the enzyme laccase on substrates such as L-3,4-dihydroxyphenylalanine (L-DOPA), the dopamine precursor.

Polyploid

Pertaining to a cell: containing more sets of chromosomes than a cell in the typical haploid (one set) or diploid (two sets) condition.

Opsonization

The binding of an antibody or other protein to the surface of a pathogen cell to target that cell for phagocytosis.

Dectin 1

(Also known as CLEC7A.) A receptor protein on the surface of immune effector cells that recognizes β-glucans on fungal cell walls to trigger an antifungal defence response.

CR3

A member of the integrin adhesion receptor family that is expressed on leukocytes. CR3 is composed of a heterodimer of CD11b (also known as αM integrin or ITGAM) and CD18 (also known as ITGB2), and recognizes fungal mannose and β-glucans.

Blood–brain barrier

A barrier that restricts the passage of solutes and microbes from the capillaries of the central nervous system into the brain. This barrier is created by capillary endothelial cells that are connected by tight junctions.

Intravital microscopy

A technique for the direct microscopic observation of cellular interactions in the tissue of an anaesthetized animal. When coupled with spinning-disk confocal microscopy, the method allows images of optical sections of cells to be collected in narrow focal planes.

Appressorium

A differentiated cell type that functions as an infection structure to mechanically penetrate the host surface; typically used by fungal pathogens to penetrate plant cell walls.

Arp2/3 complex

A heptameric protein complex that is a major component of the actin cytoskeleton; the actin-related proteins Arp2 and Arp3 function in the nucleation of new actin filaments.

WASP protein

A member of a family of proteins, named after Wiskott-Aldrich syndrome (which results from mutations in the WAS gene), that bind to and activate the Arp2/3 proteins for subsequent nucleation of actin filaments.

Intracellular proliferation rate

A measure of the relative intracellular parasitism, calculated by dividing the maximum intracellular number of fungal cells in phagocytes by the number of cells at the start of an experiment.

Serotype

A classification of cryptococcal isolates based on antibody recognition of the fungal polysaccharide capsule; Cryptococcus neoformans can be serotype A, D or AD, and Cryptococcus gattii can be serotype B or C.

Endoreplication

DNA replication without subsequent mitosis, resulting in clear doubling events for the genome.

Aneuploidy

The possession of an unusual complement of chromosomes, such as disomy arising from having two copies of a particular chromosome in a cell.

Heteroresistance

A reversible, adaptive resistance to an antimicrobial drug such that a subpopulation of cells displays the ability to grow in the presence of the drug.

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Kronstad, J., Attarian, R., Cadieux, B. et al. Expanding fungal pathogenesis: Cryptococcus breaks out of the opportunistic box. Nat Rev Microbiol 9, 193–203 (2011). https://doi.org/10.1038/nrmicro2522

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