scholarly journals Phagocytosis of Cryptococcus neoformans by, and Nonlytic Exocytosis from, Acanthamoeba castellanii

2010 ◽  
Vol 76 (18) ◽  
pp. 6056-6062 ◽  
Author(s):  
Cara J. Chrisman ◽  
Mauricio Alvarez ◽  
Arturo Casadevall
Keyword(s):  
Cryptococcus Neoformans ◽  
Virulence Factors ◽  
Acanthamoeba Castellanii ◽  
Wild Type ◽  
Pathogenic Yeast ◽  
Fungal Virulence ◽  
Environmental Interactions ◽  
Soil Amoeba ◽  
Additional Support ◽  
Mammalian Infection

ABSTRACT Cryptococcus neoformans, an encapsulated, pathogenic yeast, is endowed with a variety of virulence factors, including a polysaccharide capsule. During mammalian infection, the outcome of the interaction between C. neoformans and macrophages is central to determining the fate of the host. Previous studies have shown similarities between the interaction of C. neoformans with macrophages and with amoebae, resulting in the proposal that fungal virulence for mammals originated from selection by amoeboid predators. In this study, we investigated the interaction of C. neoformans with the soil amoeba Acanthamoeba castellanii. Comparison of phagocytic efficiency of the wild type, nonencapsulated mutants, and complemented strains showed that the capsule was antiphagocytic for amoebae. Capsular enlargement was associated with a significant reduction in phagocytosis, suggesting that this phenomenon protects against ingestion by phagocytic predators. C. neoformans var. neoformans cells were observed to exit amoebae several hours after ingestion, in a process similar to the recently described nonlytic exocytosis from macrophages. Cryptococcal exocytosis from amoebae was dependent on the strain and on actin and required fungal viability. Additionally, the presence of a capsule was inversely correlated with the likelihood of extrusion in certain strains. In summary, nonlytic exocytosis from amoebae provide another parallel to observations in fungus-macrophage interactions. These results provide additional support for the notion that some mechanisms of virulence observed during mammalian infection originated, and were selected for, by environmental interactions.

scholarly journals Superoxide Dismutase Influences the Virulence of Cryptococcus neoformans by Affecting Growth within Macrophages

2003 ◽  
Vol 71 (1) ◽  
pp. 173-180 ◽  
Author(s):  
Gary M. Cox ◽  
Thomas S. Harrison ◽  
Henry C. McDade ◽  
Carlos P. Taborda ◽  
Garrett Heinrich ◽  
...  
Keyword(s):  
Reactive Oxygen Species ◽  
Superoxide Dismutase ◽  
Cryptococcus Neoformans ◽  
Fungal Infections ◽  
Reactive Oxygen ◽  
Oxygen Species ◽  
Wild Type ◽  
Pathogenic Yeast ◽  
Antioxidant Defense Systems

ABSTRACT Superoxide dismutase (SOD) is an enzyme that converts superoxide radicals into hydrogen peroxide and molecular oxygen and has been shown to contribute to the virulence of many human-pathogenic bacteria through its ability to neutralize toxic levels of reactive oxygen species generated by the host. SOD has also been speculated to be important in the pathogenesis of fungal infections, but the role of this enzyme has not been rigorously investigated. To examine the contribution of SOD to the pathogenesis of fungal infections, we cloned the Cu,Zn SOD-encoding gene (SOD1) from the human-pathogenic yeast Cryptococcus neoformans and made mutants via targeted disruption. The sod1 mutant strains had marked decreases in SOD activity and were strikingly more susceptible to reactive oxygen species in vitro. A sod1 mutant was significantly less virulent than the wild-type strain and two independent reconstituted strains, as measured by cumulative survival in the mouse inhalational model. In vitro studies established that the sod1 strain had attenuated growth compared to the growth of the wild type and a reconstituted strain inside macrophages producing reduced amounts of nitric oxide. These findings demonstrate that (i) the Cu,Zn SOD contributes to virulence but is not required for pathogenicity in C. neoformans; (ii) the decreased virulence of the sod1 strain may be due to increased susceptibility to oxygen radicals within macrophages; and (iii) other antioxidant defense systems in C. neoformans can compensate for the loss of the Cu,Zn SOD in vivo.

scholarly journals Role of Alternative Oxidase Gene in Pathogenesis of Cryptococcus neoformans

2003 ◽  
Vol 71 (10) ◽  
pp. 5794-5802 ◽  
Author(s):  
Shamima Akhter ◽  
Henry C. McDade ◽  
Jenifer M. Gorlach ◽  
Garrett Heinrich ◽  
Gary M. Cox ◽  
...  
Keyword(s):  
Oxidative Stress ◽  
Cryptococcus Neoformans ◽  
Mutant Strain ◽  
Alternative Oxidase ◽  
Temperature Sensitive ◽  
Wild Type ◽  
Phagocytic Cells ◽  
Pathogenic Yeast ◽  
Oxidase Gene ◽  
Oxidative Pathway

ABSTRACT We identified a homologue of the alternative oxidase gene in a screen to identify genes that are preferentially transcribed in response to a shift to 37°C in the human-pathogenic yeast Cryptococcus neoformans. Alternative oxidases are nucleus-encoded mitochondrial proteins that have two putative roles: they can function in parallel with the classic cytochrome oxidative pathway to produce ATP, and they may counter oxidative stress within the mitochondria. The C. neoformans alternative oxidase gene (AOX1) was found to exist as a single copy in the genome, and it encodes a putative protein of 401 amino acids. An aox1 mutant strain was created using targeted gene disruption, and the mutant strain was reconstituted to wild type using a full-length AOX1. Compared to both the wild-type and reconstituted strains, the aox1 mutant strain was not temperature sensitive but did have significant impairment of both respiration and growth when treated with inhibitors of the classic cytochrome oxidative pathway. The aox1 mutant strain was also found to be more sensitive to the oxidative stressor tert-butyl hydroperoxide. The aox1 mutant strain was significantly less virulent than both the wild type and the reconstituted strain in the murine inhalational model, and it also had significantly impaired growth within a macrophage-like cell line. These data demonstrate that the alternative oxidase of C. neoformans can make a significant contribution to metabolism, has a role in the yeast's defense against exogenous oxidative stress, and contributes to the virulence composite of this organism, possibly by improving survival within phagocytic cells.

scholarly journals Fungal Virulence in a Lepidopteran Model Is an Emergent Property with Deterministic Features

mBio ◽  
2013 ◽  
Vol 4 (3) ◽  
Author(s):  
Monica A. Garcia-Solache ◽  
David Izquierdo-Garcia ◽  
Cameron Smith ◽  
Aviv Bergman ◽  
Arturo Casadevall
Keyword(s):  
Cryptococcus Neoformans ◽  
Virulence Factors ◽  
Galleria Mellonella ◽  
Emergent Property ◽  
Deterministic System ◽  
Pathogenic Potential ◽  
Fungal Virulence ◽  
Content Type ◽  
Cryptococcal Infection ◽  
Predictable Pattern

ABSTRACTVirulence has been proposed to be an emergent property, which by definition implies that it is not reducible to its components, but this application of a philosophical concept to the host-microbe interaction has not been experimentally tested. The goals of our study were to analyze the correlation of the phenotype with the ability to cause disease and to determine the dynamics of an experimental cryptococcal infection inGalleria mellonellaandAcanthamoeba castellanii. By studying the outcome of infection as host death, we showed that the dynamics of virulence in theG. mellonella/Cryptococcus neoformansinteraction follow a predictable pattern. We also found that the experimental temperature and not the presence of virulence factors was a critical parameter defining the pathogenic potential of cryptococcal species. Our results established that cryptococcal species not considered pathogenic could be pathogens given suitable conditions. Our results support the idea that virulence is an emergent property that cannot be easily predicted by a reductionist approach and yet it behaves as a deterministic system in a lepidopteran cryptococcal infection. These findings provide a road map for evaluating whether host-microbe interactions in other systems are chaotic, deterministic, or stochastic, including those with public health importance.IMPORTANCEVirulence is a complex phenotype that cannot be easily studied by analyzing its individual components in isolation. By studying the outcome of infection as the death of the host, we found that a given microbial phenotype does not necessarily correlate with its ability to cause disease and that the presence of so-called virulence factors does not predict pathogenicity, consistent with the notion that virulence is an emergent property. This paper reports that the dynamics of virulence inGalleria mellonellalarvae infected with the fungusCryptococcus neoformansfollows a predictable pattern. Establishing that virulence is an emergent property is important because it implies that it is not reducible to its components, and consequently, this phenomenon needs to be studied by a holistic approach.

scholarly journals Fungi pathogenic to humans: molecular bases of virulence of Candida albicans, Cryptococcus neoformans and Aspergillus fumigatus.

2009 ◽  
Vol 56 (2) ◽  
Author(s):  
Justyna Karkowska-Kuleta ◽  
Maria Rapala-Kozik ◽  
Andrzej Kozik
Keyword(s):  
Candida Albicans ◽  
Aspergillus Fumigatus ◽  
Cryptococcus Neoformans ◽  
Virulence Factors ◽  
Immunosuppressive Agents ◽  
Hydrolytic Enzymes ◽  
Host Cells ◽  
Phenotypic Switching ◽  
Human Organism ◽  
Fungal Virulence

The frequency of severe systemic fungal diseases has increased in the last few decades. The clinical use of antibacterial drugs, immunosuppressive agents after organ transplantation, cancer chemotherapy, and advances in surgery are associated with increasing risk of fungal infections. Opportunistic pathogens from the genera Candida and Aspergillus as well as pathogenic fungi from the genus Cryptococcus can invade human organism and may lead to mucosal and skin infections or to deep-seated mycoses of almost all inner organs, especially in immunocompromised patients. Nowadays, there are some effective antifungal agents, but, unfortunately, some of the pathogenic species show increasing resistance. The identification of fungal virulence factors and recognition of mechanisms of pathogenesis may lead to development of new efficient antifungal therapies. This review is focused on major virulence factors of the most common fungal pathogens of humans: Candida albicans, Aspergillus fumigatus and Cryptococcus neoformans. The adherence to host cells and tissues, secretion of hydrolytic enzymes, phenotypic switching and morphological dimorphism contribute to C. albicans virulence. The ability to grow at 37 degrees C, capsule synthesis and melanin formation are important virulence factors of C. neoformans. The putative virulence factors of A. fumigatus include production of pigments, adhesion molecules present on the cell surface and secretion of hydrolytic enzymes and toxins.

scholarly journals Cryptococcus neoformanssecretes small molecules that inhibit IL-1β inflammasome-dependent secretion

2019 ◽  
Author(s):  
Pedro Henrique Bürgel ◽  
Clara Luna Marina ◽  
Pedro H. V. Saavedra ◽  
Patrícia Albuquerque ◽  
Paulo Henrique Holanda ◽  
...  
Keyword(s):  
Lactic Acid ◽  
Cryptococcus Neoformans ◽  
Type Strain ◽  
Wild Type Strain ◽  
Conditioned Media ◽  
Inflammasome Activation ◽  
Wild Type ◽  
Fungal Virulence ◽  
The Impact

AbstractCryptococcus neoformansis an encapsulated yeast that causes disease mainly in immunosuppressed hosts. It is considered a facultative intracellular pathogen because of its capacity to survive and replicate inside phagocytes, especially macrophages. This capacity is heavily dependent on various virulence factors, particularly the glucuronoxylomannan (GXM) component of the polysaccharide capsule, that render the non- or poorly-activated macrophage ineffective against phagocytosed yeast. Strategies utilized by macrophages to prevent this scenario include pyroptosis (a rapid highly inflammatory cell death) and vomocytosis (the expulsion of the pathogen from the intracellular environment without lysis). Inflammasome activation in phagocytes is usually protective against fungal infections, including cryptococcosis. Nevertheless, recognition ofC. neoformansby inflammasome receptors requires specific changes in morphology or the opsonization of the yeast, impairing a proper inflammasome function. In this context, we analyzed the impact of molecules secreted byC. neoformansB3501 strain and its acapsular mutantΔcap67in an inflammasome activationin vitromodel. Our results showed that conditioned media derived from B3501 was capable of inhibiting inflammasome dependent events (i. e. IL-1β secretion and LDH release via pyroptosis) more strongly than conditioned media fromΔcap67, regardless of GXM presence. We also demonstrated that macrophages treated with conditioned media were less responsive against infection with the virulent strain H99, exhibiting lower rates of phagocytosis, increased fungal burdens and enhanced vomocytosis. Moreover, we showed that the aromatic metabolite DL-Indole-3-lactic acid (ILA) was present in B3501’s conditioned media and that this fungal metabolite is involved in the regulation of inflammasome activation byC. neoformans. Overall, the results presented show that conditioned media from a wild-type strain can inhibit an important recognition pathway and subsequent fungicidal functions of macrophages, contributing to fungal survivalin vitroand suggesting that this serves as an important role for secreted molecules during cryptococcal infections.Author’s SummaryCryptococcus neoformansis the agent of cryptococcal meningitis, a disease that can be life-threatening in immunocompromised hosts such as those infected with HIV. The infection thrives in hosts that poorly activate their immune system, mainly because of the yeast’s ability to survive inside macrophages and migrate towards the central nervous system. Emerging data indicate that cryptococci modulate the host immune response, but the underlying mechanisms remain largely uncharacterized. Here we show that secreted molecules from a wild-type strain ofC. neoformansimpair inflammatory responses driven by inflammasome activation, which in turn impact the macrophage antifungal activity. We further show that this inhibition does not involve GXM, the main constituent of the fungal capsule, but rather is partially dependent on DL-Indole-3-lactic acid (ILA), a metabolite not previously implicated in fungal virulence.

scholarly journals Molecular Genetic Analyses of Mating Pheromones Reveal Intervariety Mating or Hybridization in Cryptococcus neoformans

2002 ◽  
Vol 70 (9) ◽  
pp. 5225-5235 ◽  
Author(s):  
Vishnu Chaturvedi ◽  
Jinjiang Fan ◽  
Birgit Stein ◽  
Melissa J. Behr ◽  
William A. Samsonoff ◽  
...  
Keyword(s):  
Cryptococcus Neoformans ◽  
Phylogenetic Analyses ◽  
Molecular Genetic ◽  
Purifying Selection ◽  
Neutral Evolution ◽  
Nucleotide Polymorphisms ◽  
Pathogenic Yeast ◽  
Fungal Virulence ◽  
Mating Pheromones ◽  
Copy Numbers

ABSTRACT The sexual mating of the pathogenic yeast Cryptococcus neoformans is important for pathogenesis studies because the fungal virulence is linked to the α mating type (MATα). We characterized C. neoformans mating pheromones (MFα 1 and MFa1) from 122 strains to understand intervariety hybridization or mating and intervariety virulence. MFα 1 in three C. neoformans varieties showed (a) specific nucleotide polymorphisms, (b) different copy numbers and chromosomal localizations, and (c) unique deduced amino acids in two geographic populations of C. neoformans var. gattii. MFα 1 of different varieties cross-hybridized in Southern hybridizations. Their phylogenetic analyses showed purifying selection (neutral evolution). These observations suggested that MATα strains from any of the three C. neoformans varieties could mate or hybridize in nature with MAT a strains of C. neoformans var. neoformans. A few serotype A/D diploid strains provided evidence for mating or hybridization, while a majority of A/D strains tested positive for haploid MFα 1 identical to that of C. neoformans var. grubii. MFα 1 sequence and copy numbers in diploids were identical to those of C. neoformans var. grubii, while their MFa1 sequences were identical to those of C. neoformans var. neoformans; thus, these strains were hybrids. The mice survival curves and histological lesions revealed A/D diploids to be highly pathogenic, with pathogenicity levels similar to that of the C. neoformans var. grubii type strain and unlike the low pathogenicity levels of C. neoformans var. neoformans strains. In contrast to MFα 1 in three varieties, MFa1 amplicons and hybridization signals could be obtained only from two C. neoformans var. neoformans reference strains and eight A/D diploids. This suggested that a yet undiscovered MFa pheromone(s) in C. neoformans var. gattii and C. neoformans var. grubii is unrelated to, highly divergent from, or rarer than that in C. neoformans var. neoformans. These observations could form the basis for future studies on the role of intervariety mating in C. neoformans biology and virulence.

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