scholarly journals Loss of Allergen 1 Confers a Hypervirulent Phenotype That Resembles Mucoid Switch Variants of Cryptococcus neoformans

2008 ◽  
Vol 77 (1) ◽  
pp. 128-140 ◽  
Author(s):  
Neena Jain ◽  
Li Li ◽  
Ye-Ping Hsueh ◽  
Abraham Guerrero ◽  
Joseph Heitman ◽  
...  
Keyword(s):  
Intracranial Pressure ◽  
Cryptococcus Neoformans ◽  
Gene Function ◽  
Pathogenic Fungus ◽  
Opportunistic Pathogen ◽  
Phenotypic Switching ◽  
Elevated Intracranial Pressure ◽  
Macrophage Phagocytosis ◽  
Switch Variant

ABSTRACT Microbial survival in a host is usually dependent on the ability of a pathogen to undergo changes that promote escape from host defense mechanisms. The human-pathogenic fungus Cryptococcus neoformans undergoes phenotypic switching in vivo that promotes persistence in tissue. By microarray and real-time PCR analyses, the allergen 1 gene (ALL1) was found to be downregulated in the hypervirulent mucoid switch variant, both during logarithmic growth and during intracellular growth in macrophages. The ALL1 gene encodes a small cytoplasmic protein that is involved in capsule formation. Growth of an all1Δ gene deletion mutant was normal. Similar to cells of the mucoid switch variant, all1Δ cells produced a larger polysaccharide capsule than cells of the smooth parent and the complemented strain produced, and the enlarged capsule inhibited macrophage phagocytosis. The mutant exhibited a modest defect in capsule induction compared to all of the other variants. In animal models the phenotype of the all1Δ mutant mimicked the hypervirulent phenotype of the mucoid switch variant, which is characterized by decreased host survival and elevated intracranial pressure. Decreased survival is likely the result of both an ineffective cell-mediated immune response and impaired phagocytosis by macrophages. Consequently, we concluded that, unlike loss of most virulence-associated genes, where loss of gene function results in attenuated virulence, loss of the ALL1 gene enhances virulence by altering the host-pathogen interaction and thereby impairing clearance. Our data identified the first cryptococcal gene associated with elevated intracranial pressure and support the hypothesis that an environmental opportunistic pathogen has modified its virulence in vivo by epigenetic downregulation of gene function.

scholarly journals Induction of Capsule Growth in Cryptococcus neoformans by Mammalian Serum and CO2

2003 ◽  
Vol 71 (11) ◽  
pp. 6155-6164 ◽  
Author(s):  
Oscar Zaragoza ◽  
Bettina C. Fries ◽  
Arturo Casadevall
Keyword(s):  
Cyclic Amp ◽  
Cryptococcus Neoformans ◽  
Pathogenic Fungus ◽  
Phenotypic Switching ◽  
Considerable Variability ◽  
Highly Efficient ◽  
Camp Pathway ◽  
Animal Infection ◽  
Capsule Size

ABSTRACT The pathogenic fungus Cryptococcus neoformans has a polysaccharide capsule that is essential for virulence in vivo. Capsule size is known to increase during animal infection, and this phenomenon was recently associated with virulence. Although various conditions have been implicated in promoting capsule growth, including CO2 concentration, osmolarity, and phenotypic switching, it is difficult to reproduce the capsule enlargement effect in the laboratory. In this study, we report that serum can induce capsule growth, and we describe the conditions that induce this effect, not only by serum but also by CO2. Capsule enlargement was dependent on the medium used, and this determined whether the strain responded to serum or CO2 efficiently. Serum was most effective in inducing capsule growth under nutrient-limited conditions. There was considerable variability between strains in their response to either serum or CO2, with some strains requiring both stimuli. Sera from several animal sources were each highly efficient in inducing capsule growth. The cyclic AMP (cAMP) pathway and Ras1 were both necessary for serum-induced capsule growth. The lack of induction in the ras1 mutant was not complemented by exogenous cAMP, indicating that these pathways act in parallel. However, both cAMP and Ras1 were dispensable for inducing a partial capsule growth by CO2, suggesting that multiple pathways participate in this process. The ability of serum to induce capsule growth suggests a mechanism for the capsular enlargement observed during animal infection.

scholarly journals Isolation and Characterization of Senescent Cryptococcus neoformans and Implications for Phenotypic Switching and Pathogenesis in Chronic Cryptococcosis

2009 ◽  
Vol 8 (6) ◽  
pp. 858-866 ◽  
Author(s):  
Neena Jain ◽  
Emily Cook ◽  
Immaculata Xess ◽  
Fahmi Hasan ◽  
Dietrich Fries ◽  
...  
Keyword(s):  
Mathematical Modeling ◽  
Cryptococcus Neoformans ◽  
Chronic Infection ◽  
Yeast Cells ◽  
Phenotypic Switching ◽  
Isolation And Characterization ◽  
Immunocompromised Hosts ◽  
Infection Experiments

ABSTRACT Although several virulence factors and associated genes have been identified, the mechanisms that allow Cryptococcus neoformans to adapt during chronic infection and to persist in immunocompromised hosts remain poorly understood. Characterization of senescent cells of C. neoformans demonstrated that these cells exhibit a significantly enlarged cell body and capsule but still cross the blood-brain barrier. C. neoformans cells with advanced generational age are also more resistant to phagocytosis and killing by antifungals, which could promote their selection during chronic disease in humans. Senescent cells of RC-2, a C. neoformans strain that undergoes phenotypic switching, manifest switching rates up to 11-fold higher than those of younger cells. Infection experiments with labeled cells suggest that senescent yeast cells can potentially accumulate in vivo. Mathematical modeling incorporating different switching rates demonstrates how increased switching rates promote the emergence of hypervirulent mucoid variants during chronic infection. Our findings introduce the intriguing concept that senescence in eukaryotic pathogens could be a mechanism of microevolution that may promote pathoadaptation and facilitate evasion of an evolving immune response.

scholarly journals Phenotypic Switching in a Cryptococcus neoformans Variety gattii Strain Is Associated with Changes in Virulence and Promotes Dissemination to the Central Nervous System

2006 ◽  
Vol 74 (2) ◽  
pp. 896-903 ◽  
Author(s):  
N. Jain ◽  
Li Li ◽  
D. C. McFadden ◽  
U. Banarjee ◽  
X. Wang ◽  
...  
Keyword(s):  
Cryptococcus Neoformans ◽  
Pulmonary Infection ◽  
Colony Morphology ◽  
Phenotypic Switching ◽  
Pathogen Population ◽  
Infection Models ◽  
Polysaccharide Capsule ◽  
The Central Nervous System ◽  
Serotype B

ABSTRACT This is the first report of a Cryptococcus neoformans var. gattii strain (serotype B) that switches reversibly between its parent mucoid (NP1-MC) colony morphology and a smooth (NP1-SM) colony morphology. Similar to C. neoformans var. grubii and C. neoformans var. neoformans strains, the switch is associated with changes in the polysaccharide capsule and virulence in animal models. In murine infection models, NP1-MC is significantly more virulent than NP1-SM (P < 0.021). In contrast to the serotype A and D strains, the serotype B strain switches in vivo reversibly between both colony morphologies. The polysaccharide of NP1-MC exhibits a thicker capsule, and thus NP1-MC exhibits enhanced intracellular survival in macrophages. Consistent with this finding, switching to the mucoid variant is observed in pulmonary infection with NP1-SM. In contrast, the thin polysaccharide capsule of NP1-SM permits better crossing of the blood-brain barrier. In this regard, only smooth colonies were grown from brain homogenates of NP1-MC-infected mice. Our findings have important implications for the pathogenesis of cryptococcosis and suggest that phenotypic switching affects host-pathogen interactions in the local microenvironment. This altered interaction then selects for specific colony variants to arise in a pathogen population.

scholarly journals Role for Chitin and Chitooligomers in the Capsular Architecture of Cryptococcus neoformans

2009 ◽  
Vol 8 (10) ◽  
pp. 1543-1553 ◽  
Author(s):  
Fernanda L. Fonseca ◽  
Leonardo Nimrichter ◽  
Radames J. B. Cordero ◽  
Susana Frases ◽  
Jessica Rodrigues ◽  
...  
Keyword(s):  
Cell Wall ◽  
Cryptococcus Neoformans ◽  
Pathogenic Fungus ◽  
Monosaccharide Composition ◽  
Altered Expression ◽  
Functional Activities ◽  
Differential Reactivity ◽  
Human Pathogenic Fungus

ABSTRACT Molecules composed of β-1,4-linked N-acetylglucosamine (GlcNAc) and deacetylated glucosamine units play key roles as surface constituents of the human pathogenic fungus Cryptococcus neoformans. GlcNAc is the monomeric unit of chitin and chitooligomers, which participate in the connection of capsular polysaccharides to the cryptococcal cell wall. In the present study, we evaluated the role of GlcNAc-containing structures in the assembly of the cryptococcal capsule. The in vivo expression of chitooligomers in C. neoformans varied depending on the infected tissue, as inferred from the differential reactivity of yeast forms to the wheat germ agglutinin (WGA) in infected brain and lungs of rats. Chromatographic and dynamic light-scattering analyses demonstrated that glucuronoxylomannan (GXM), the major cryptococcal capsular component, interacts with chitin and chitooligomers. When added to C. neoformans cultures, chitooligomers formed soluble complexes with GXM and interfered in capsular assembly, as manifested by aberrant capsules with defective connections with the cell wall and no reactivity with a monoclonal antibody to GXM. Cultivation of C. neoformans in the presence of an inhibitor of glucosamine 6-phosphate synthase resulted in altered expression of cell wall chitin. These cells formed capsules that were loosely connected to the cryptococcal wall and contained fibers with decreased diameters and altered monosaccharide composition. These results contribute to our understanding of the role played by chitin and chitooligosaccharides on the cryptococcal capsular structure, broadening the functional activities attributed to GlcNAc-containing structures in this biological system.

scholarly journals Phenotypic switching in Cryptococcus neoformans

Microbiology ◽  
2006 ◽  
Vol 152 (1) ◽  
pp. 3-9 ◽  
Author(s):  
A. Guerrero ◽  
N. Jain ◽  
D. L. Goldman ◽  
B. C. Fries
Keyword(s):  
Gene Expression ◽  
Cryptococcus Neoformans ◽  
Chronic Infection ◽  
Inflammatory Responses ◽  
Phenotypic Switching ◽  
Phenotypic Switch ◽  
Intracerebral Pressure ◽  
Differential Gene ◽  
Selection Of

Phenotypic switching has been described in serotype A and D strains of Cryptococcus neoformans. It occurs in vivo during chronic infection and is associated with differential gene expression and changes in virulence. The switch involves changes in the polysaccharide capsule and cell wall that affect the yeast's ability to resist phagocytosis. In addition, the phenotypic switch variants elicit qualitatively different inflammatory responses in the host. In animal models of chronic cryptococosis, the immune response of the host ultimately determines which of the switch variants are selected and maintained. The importance of phenotypic switching is further underscored by several findings that are relevant in the setting of human disease. These include the ability of the mucoid colony variant of RC-2 (RC-2 MC) but not the smooth variant (RC-2 SM) to promote increased intracerebral pressure in a rat model of cryptococcal meningitis. Furthermore, chemotherapeutic and immunological antifungal interventions can promote the selection of the RC-2 MC variant during chronic murine infection.

scholarly journals Phenotypic switching of Cryptococcus neoformans occurs in vivo and influences the outcome of infection

2001 ◽  
Vol 108 (11) ◽  
pp. 1639-1648 ◽  
Author(s):  
Bettina C. Fries ◽  
Carlos P. Taborda ◽  
Evan Serfass ◽  
Arturo Casadevall
Keyword(s):  
Cryptococcus Neoformans ◽  
Phenotypic Switching

scholarly journals Cryptococcus neoformans melanization incorporates multiple catecholamines to produce polytypic melanin

2021 ◽  
Author(s):  
Rosanna P. Baker ◽  
Christine Chrissian ◽  
Ruth E. Stark ◽  
Arturo Casadevall
Keyword(s):  
Cryptococcus Neoformans ◽  
Brain Tissue ◽  
Pathogenic Fungus ◽  
Structural Complexity ◽  
Pathogenic Fungi ◽  
Human Infection ◽  
Melanin Pigment ◽  
Practical Standpoint ◽  
Human Pathogenic Fungus

AbstractMelanin is a major virulence factor in pathogenic fungi that enhances the ability of fungal cells to resist immune clearance. Cryptococcus neoformans is an important human pathogenic fungus that synthesizes melanin from exogenous tissue catecholamine precursors during infection, but the type of melanin made in cryptococcal meningoencephalitis is unknown. We analyzed the efficacy of various catecholamines found in brain tissue in supporting melanization using animal brain tissue and synthetic catecholamine mixtures reflecting brain tissue proportions. Solid-state NMR spectra of the melanin pigment produced from such mixtures displayed larger melanin contributions than expected from the most robust dopamine constituent, suggesting uptake of additional catecholamines. Probing the biosynthesis of melanin using radiolabeled catecholamines revealed that C. neoformans melanization simultaneously incorporated more than one catecholamine, implying that the pigment was polytypic in nature. Nonetheless, melanin derived from individual or mixed catecholamines had comparable ability to protect C. neoformans against ultraviolet light and oxidants. Our results indicate that melanin produced during infection differs depending on the catecholamine composition of tissue and that melanin pigment synthesized in vivo is likely to accrue from the polymerization of a mixture of precursors. From a practical standpoint our results strongly suggest that using dopamine as a polymerization precursor is capable of producing melanin pigment comparable to that produced during infection. On a more fundamental level our findings uncover additional structural complexity for natural cryptococcal melanin by demonstrating that pigment produced during human infection is likely to be composed of polymerized moieties derived from chemically different precursors.

scholarly journals Biosynthesis of UDP-GlcA, a key metabolite for capsular polysaccharide synthesis in the pathogenic fungus Cryptococcus neoformans

2004 ◽  
Vol 381 (1) ◽  
pp. 131-136 ◽  
Author(s):  
Maor BAR-PELED ◽  
Cara L. GRIFFITH ◽  
Jeramia J. ORY ◽  
Tamara L. DOERING
Keyword(s):  
Cryptococcus Neoformans ◽  
Capsular Polysaccharide ◽  
Pathogenic Fungus ◽  
Glucose Dehydrogenase ◽  
Opportunistic Pathogen ◽  
Wild Type ◽  
Gene Encoding ◽  
Glucose Binding ◽  
Polysaccharide Synthesis ◽  
Important Enzyme

UDP-glucose dehydrogenase catalyses the conversion of UDP-glucose into UDP-GlcA, a critical precursor for glycan synthesis across evolution. We have cloned the gene encoding this important enzyme from the opportunistic pathogen Cryptococcus neoformans. In this fungus, UDP-GlcA is required for the synthesis of capsule polysaccharides, which in turn are essential for virulence. The gene was expressed in Escherichia coli and the 51.3-kDa recombinant protein from wild-type and five mutants was purified for analysis. The cryptococcal enzyme is strongly inhibited by UDP-xylose and NADH, has highest activity at pH 7.5 and demonstrates Km (app) values of 0.1 and 1.5 mM for NAD+ and UDP-glucose respectively. Its activity was significantly decreased by mutations in the putative sites of NAD+ and UDP-glucose binding. Unlike previously reported eukaryotic UDP-glucose dehydrogenases, which are hexamers, the cryptococcal enzyme is a dimer.

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