Article

The fatal fungal outbreak on Vancouver Island is characterized by enhanced intracellular parasitism driven by mitochondrial regulation.

School of Biosciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom.
Proceedings of the National Academy of Sciences (Impact Factor: 9.81). 08/2009; 106(31):12980-5. DOI: 10.1073/pnas.0902963106
Source: PubMed

ABSTRACT In 1999, the population of Vancouver Island, Canada, began to experience an outbreak of a fatal fungal disease caused by a highly virulent lineage of Cryptococcus gattii. This organism has recently spread to the Canadian mainland and Pacific Northwest, but the molecular cause of the outbreak remains unknown. Here we show that the Vancouver Island outbreak (VIO) isolates have dramatically increased their ability to replicate within macrophages of the mammalian immune system in comparison with other C. gattii strains. We further demonstrate that such enhanced intracellular parasitism is directly linked to virulence in a murine model of cryptococcosis, suggesting that this phenotype may be the cause of the outbreak. Finally, microarray studies on 24 C. gattii strains reveals that the hypervirulence of the VIO isolates is characterized by the up-regulation of a large group of genes, many of which are encoded by mitochondrial genome or associated with mitochondrial activities. This expression profile correlates with an unusual mitochondrial morphology exhibited by the VIO strains after phagocytosis. Our data thus demonstrate that the intracellular parasitism of macrophages is a key driver of a human disease outbreak, a finding that has significant implications for a wide range of other human pathogens.

1 Bookmark
 · 
91 Views
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Candida species exhibit a variety of ploidies and modes of sexual reproduction. Most species possess the requisite genes for sexual reproduction, recombination, and meiosis, yet only a few have been reported to undergo a complete sexual cycle including mating and sporulation. Candida albicans, the most studied Candida species and a prevalent human fungal pathogen, completes its sexual cycle via a parasexual process of concerted chromosome loss rather than a conventional meiosis. In this study, we examine ploidy changes in Candida tropicalis, a closely related species to C. albicans that was recently revealed to undergo sexual mating. C. tropicalis diploid cells mate to form tetraploid cells, and we show that these can be induced to undergo chromosome loss to regenerate diploid forms by growth on sorbose medium. The diploid products are themselves mating-competent, thereby establishing a parasexual cycle in this species for the first time. Extended incubation (>120 generations) of C. tropicalis tetraploid cells in rich culture conditions also resulted in instability of the tetraploid form and a gradual reduction in ploidy back to the diploid state. The fitness of C. tropicalis diploid and tetraploid cells were compared and diploid cells exhibited increased fitness relative to tetraploid cells in vitro, despite diploid and tetraploid cells having similar doubling times. Collectively, these experiments demonstrate distinct pathways by which a parasexual cycle can occur in C. tropicalis, and indicate that non-meiotic mechanisms drive ploidy changes in this prevalent human pathogen.
    Eukaryotic Cell 10/2013; · 3.59 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Mitochondria are eukaryotic organelles supporting individual life-style via generation of proton motive force and cellular energy, and indispensable metabolic pathways. As part of genome sequencing of the white rot Basidiomycota species Phlebia radiata, we first assembled its mitochondrial genome (mtDNA). So far, the 156 348 bp mtDNA is the second largest described for fungi, and of considerable size among eukaryotes. The P. radiata mtDNA assembled as single circular dsDNA molecule containing genes for the large and small ribosomal RNAs, 28 transfer RNAs, and over 100 open reading frames encoding the 14 fungal conserved protein subunits of the mitochondrial complexes I, III, IV, and V. Two genes (atp6 and tRNA-IleGAU) were duplicated within 6.1 kbp inverted region, which is a unique feature of the genome. The large mtDNA size, however, is explained by the dominance of intronic and intergenic regions (sum 80% of mtDNA sequence). The intergenic DNA stretches harness short (≤200 nt) repetitive, dispersed and overlapping sequence elements in abundance. Long self-splicing introns of types I and II interrupt eleven of the conserved genes (cox1,2,3; cob; nad1,2,4,4L,5; rnl; rns). The introns embrace a total of 57 homing endonucleases with LAGLIDADGD and GYI-YIG core motifs, which makes P. radiata mtDNA to one of the largest known reservoirs of intron-homing endonucleases. The inverted duplication, intergenic stretches, and intronic features are indications of dynamics and genetic flexibility of the mtDNA, not fully recognized to this extent in fungal mitochondrial genomes previously, thus giving new insights for the evolution of organelle genomes in eukaryotes.
    PLoS ONE 01/2014; 9(5):e97141. · 3.53 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Background. Cryptococcal meningitis (CM) is a leading cause of HIV-associated mortality globally. High fungal burden in cerebrospinal fluid (CSF) at diagnosis and poor fungal clearance during treatment are recognized adverse prognostic markers; however, the underlying pathogenic factors that drive these clinical manifestations are incompletely understood. We profiled a large set of clinical isolates for established cryptococcal virulence traits to evaluate the contribution of C. neoformans phenotypic diversity to clinical presentation and outcome in human cryptococcosis. Methods. Sixty-five C. neoformans isolates from clinical trial patients with matched clinical data were assayed in vitro to determine murine macrophage uptake, intracellular proliferation rate (IPR), capsule induction, and laccase activity. Analysis of the correlation between prognostic clinical and host immune parameters and fungal phenotypes was performed using Spearman's r, while the fungal-dependent impact on long-term survival was determined by Cox regression analysis. Results. High levels of fungal uptake by macrophages in vitro, but not the IPR, were associated with CSF fungal burden (r = 0.38, P = 0.002) and long-term patient survival (hazard ratio [HR] 2.6, 95% CI 1.2-5.5, P = 0.012). High-uptake strains were hypocapsular (r = -0.28, P = 0.05) and exhibited enhanced laccase activity (r = 0.36, P = 0.003). Fungal isolates with greater laccase activity exhibited heightened survival ex vivo in purified CSF (r = 0.49, P < 0.0001) and resistance to clearance following patient antifungal treatment (r = 0.39, P = 0.003). Conclusion. These findings underscore the contribution of cryptococcal-phagocyte interactions and laccase-dependent melanin pathways to human clinical presentation and outcome. Furthermore, characterization of fungal-specific pathways that drive clinical manifestation provide potential targets for the development of therapeutics and the management of CM. Funding. This work was made possible by funding from the Wellcome Trust (WT088148MF), the Medical Research Council (MR/J008176/1), the NIHR Surgical Reconstruction and Microbiology Research Centre and the Lister Institute for Preventive Medicine (to R.C. May), and a Wellcome Trust Intermediate fellowship (089966, to T. Bicanic). The C. neoformans isolates were collected within clinical trials funded by the British Infection Society (fellowship to T. Bicanic), the Wellcome Trust (research training fellowships WT069991, to A.E. Brouwer and WT081794, to J.N. Jarvis), and the Medical Research Council, United Kingdom (76201). The funding sources had no role in the design or conduct of this study, nor in preparation of the manuscript.
    The Journal of clinical investigation 04/2014; · 15.39 Impact Factor

Full-text (2 Sources)

View
34 Downloads
Available from
May 29, 2014