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Navarro-Mendoza MI, Pérez-Arques C, Parker J, Xu Z, Kelly S, Heitman J. Alternative ergosterol biosynthetic pathways confer antifungal drug resistance in the human pathogens within the Mucor species complex. mBio 2024; 15:e0166124. [PMID: 38980037 PMCID: PMC11323496 DOI: 10.1128/mbio.01661-24] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2024] [Accepted: 06/18/2024] [Indexed: 07/10/2024] Open
Abstract
Mucormycoses are emerging fungal infections caused by a variety of heterogeneous species within the Mucorales order. Among the Mucor species complex, Mucor circinelloides is the most frequently isolated pathogen in mucormycosis patients and despite its clinical significance, there is an absence of established genome manipulation techniques to conduct molecular pathogenesis studies. In this study, we generated a spontaneous uracil auxotrophic strain and developed a genetic transformation procedure to analyze molecular mechanisms conferring antifungal drug resistance. With this new model, phenotypic analyses of gene deletion mutants were conducted to define Erg3 and Erg6a as key biosynthetic enzymes in the M. circinelloides ergosterol pathway. Erg3 is a C-5 sterol desaturase involved in growth, sporulation, virulence, and azole susceptibility. In other fungal pathogens, erg3 mutations confer azole resistance because Erg3 catalyzes the production of a toxic diol upon azole exposure. Surprisingly, M. circinelloides produces only trace amounts of this toxic diol and yet, it is still susceptible to posaconazole and isavuconazole due to alterations in membrane sterol composition. These alterations are severely aggravated by erg3Δ mutations, resulting in ergosterol depletion and, consequently, hypersusceptibility to azoles. We also identified Erg6a as the main C-24 sterol methyltransferase, whose activity may be partially rescued by the paralogs Erg6b and Erg6c. Loss of Erg6a function diverts ergosterol synthesis to the production of cholesta-type sterols, resulting in resistance to amphotericin B. Our findings suggest that mutations or epimutations causing loss of Erg6 function may arise during human infections, resulting in antifungal drug resistance to first-line treatments against mucormycosis. IMPORTANCE The Mucor species complex comprises a variety of opportunistic pathogens known to cause mucormycosis, a potentially lethal fungal infection with limited therapeutic options. The only effective first-line treatments against mucormycosis consist of liposomal formulations of amphotericin B and the triazoles posaconazole and isavuconazole, all of which target components within the ergosterol biosynthetic pathway. This study uncovered M. circinelloides Erg3 and Erg6a as key enzymes to produce ergosterol, a vital constituent of fungal membranes. Absence of any of those enzymes leads to decreased ergosterol and consequently, resistance to ergosterol-binding polyenes such as amphotericin B. Particularly, losing Erg6a function poses a higher threat as the ergosterol pathway is channeled into alternative sterols similar to cholesterol, which maintain membrane permeability. As a result, erg6a mutants survive within the host and disseminate the infection, indicating that Erg6a deficiency may arise during human infections and confer resistance to the most effective treatment against mucormycoses.
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Affiliation(s)
- María Isabel Navarro-Mendoza
- Department of Molecular Genetics and Microbiology, Duke University School of Medicine, Durham, North Carolina, USA
| | - Carlos Pérez-Arques
- Department of Molecular Genetics and Microbiology, Duke University School of Medicine, Durham, North Carolina, USA
| | - Josie Parker
- Molecular Biosciences Division, School of Biosciences, Cardiff University, Cardiff, Wales, United Kingdom
| | - Ziyan Xu
- Department of Molecular Genetics and Microbiology, Duke University School of Medicine, Durham, North Carolina, USA
| | - Steven Kelly
- Institute of Life Science, Swansea University Medical School, Swansea, Wales, United Kingdom
| | - Joseph Heitman
- Department of Molecular Genetics and Microbiology, Duke University School of Medicine, Durham, North Carolina, USA
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Sepúlveda VE, Goldman WE, Matute DR. Genotypic diversity, virulence, and molecular genetic tools in Histoplasma. Microbiol Mol Biol Rev 2024; 88:e0007623. [PMID: 38819148 DOI: 10.1128/mmbr.00076-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/01/2024] Open
Abstract
SUMMARYHistoplasmosis is arguably the most common fungal respiratory infection worldwide, with hundreds of thousands of new infections occurring annually in the United States alone. The infection can progress in the lung or disseminate to visceral organs and can be difficult to treat with antifungal drugs. Histoplasma, the causative agent of the disease, is a pathogenic fungus that causes life-threatening lung infections and is globally distributed. The fungus has the ability to germinate from conidia into either hyphal (mold) or yeast form, depending on the environmental temperature. This transition also regulates virulence. Histoplasma and histoplasmosis have been classified as being of emergent importance, and in 2022, the World Health Organization included Histoplasma as 1 of the 19 most concerning human fungal pathogens. In this review, we synthesize the current understanding of the ecological niche, evolutionary history, and virulence strategies of Histoplasma. We also describe general patterns of the symptomatology and epidemiology of histoplasmosis. We underscore areas where research is sorely needed and highlight research avenues that have been productive.
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Affiliation(s)
- Victoria E Sepúlveda
- Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA
| | - William E Goldman
- Department of Microbiology and Immunology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA
| | - Daniel R Matute
- Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA
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3
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Navarro-Mendoza MI, Pérez-Arques C, Parker J, Xu Z, Kelly S, Heitman J. Alternative ergosterol biosynthetic pathways confer antifungal drug resistance in the human pathogens within the Mucor species complex. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2023.12.01.569667. [PMID: 38076934 PMCID: PMC10705545 DOI: 10.1101/2023.12.01.569667] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2024]
Abstract
Mucormycoses are emerging fungal infections caused by a variety of heterogeneous species within the Mucorales order. Among the Mucor species complex, Mucor circinelloides is the most frequently isolated pathogen in mucormycosis patients and despite its clinical significance, there is an absence of established genome manipulation techniques to conduct molecular pathogenesis studies. In this study, we generated a spontaneous uracil auxotrophic strain and developed a genetic transformation procedure to analyze molecular mechanisms conferring antifungal drug resistance. With this new model, phenotypic analyses of gene deletion mutants were conducted to define Erg3 and Erg6a as key biosynthetic enzymes in the M. circinelloides ergosterol pathway. Erg3 is a C-5 sterol desaturase involved in growth, sporulation, virulence, and azole susceptibility. In other fungal pathogens, erg3 mutations confer azole resistance because Erg3 catalyzes the production of a toxic diol upon azole exposure. Surprisingly, M. circinelloides produces only trace amounts of this toxic diol and yet, it is still susceptible to posaconazole and isavuconazole due to alterations in membrane sterol composition. These alterations are severely aggravated by erg3Δ mutations, resulting in ergosterol depletion and consequently, hypersusceptibility to azoles. We also identified Erg6a as the main C-24 sterol methyltransferase, whose activity may be partially rescued by the paralogs Erg6b and Erg6c. Loss of Erg6a function diverts ergosterol synthesis to the production of cholesta-type sterols, resulting in resistance to amphotericin B. Our findings suggest that mutations or epimutations causing loss of Erg6 function may arise during human infections, resulting in antifungal drug resistance to first-line treatments against mucormycosis.
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4
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Buil JB, Oliver JD, Law D, Baltussen T, Zoll J, Hokken MWJ, Tehupeiory-Kooreman M, Melchers WJG, Birch M, Verweij PE. Resistance profiling of Aspergillus fumigatus to olorofim indicates absence of intrinsic resistance and unveils the molecular mechanisms of acquired olorofim resistance. Emerg Microbes Infect 2022; 11:703-714. [PMID: 35109772 PMCID: PMC8890541 DOI: 10.1080/22221751.2022.2034485] [Citation(s) in RCA: 16] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Olorofim (F901318) is a new antifungal currently under clinical development that shows both in vitro and in vivo activity against a number of filamentous fungi including Aspergillus fumigatus. In this study, we screened A. fumigatus isolates for intrinsic olorofim-resistant A. fumigatus and evaluated the ability of A. fumigatus to acquire an olorofim-resistant phenotype. No intrinsic resistance was found in 975 clinical A. fumigatus isolates. However, we found that isolates with increased olorofim MICs (> 8 mg/L) could be selected using a high number of conidia and olorofim exposure under laboratory conditions. Assessment of the frequency of acquired olorofim resistance development of A. fumigatus was shown to be higher than for voriconazole but lower than for itraconazole. Sequencing the PyrE gene of isogenic isolates with olorofim MICs of >8 mg/L identified various amino acid substitutions with a hotspot at locus G119. Olorofim was shown to have reduced affinity to mutated target protein dihydroorotate dehydrogenase (DHODH) and the effect of these mutations was proven by introducing the mutations directly in A. fumigatus. We then investigated whether G119 mutations were associated with a fitness cost in A. fumigatus. These experiments showed a small but significant reduction in growth rate for strains with a G119V substitution, while strains with a G119C substitution did not exhibit a reduction in growth rate. These in vitro findings were confirmed in an in vivo pathogenicity model.
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Affiliation(s)
- Jochem B Buil
- Department of Medical Microbiology, Radboud University Medical Center, Nijmegen, The Netherlands.,Radboudumc-CWZ Center of Expertise for Mycology, Nijmegen, The Netherlands
| | | | - Derek Law
- F2G Ltd, Lankro Way, Manchester, United Kingdom
| | - Tim Baltussen
- Department of Medical Microbiology, Radboud University Medical Center, Nijmegen, The Netherlands
| | - Jan Zoll
- Department of Medical Microbiology, Radboud University Medical Center, Nijmegen, The Netherlands.,Radboudumc-CWZ Center of Expertise for Mycology, Nijmegen, The Netherlands
| | - Margriet W J Hokken
- Department of Medical Microbiology, Radboud University Medical Center, Nijmegen, The Netherlands
| | - Marlou Tehupeiory-Kooreman
- Department of Medical Microbiology, Radboud University Medical Center, Nijmegen, The Netherlands.,Radboudumc-CWZ Center of Expertise for Mycology, Nijmegen, The Netherlands
| | - Willem J G Melchers
- Department of Medical Microbiology, Radboud University Medical Center, Nijmegen, The Netherlands.,Radboudumc-CWZ Center of Expertise for Mycology, Nijmegen, The Netherlands
| | - Mike Birch
- F2G Ltd, Lankro Way, Manchester, United Kingdom
| | - Paul E Verweij
- Department of Medical Microbiology, Radboud University Medical Center, Nijmegen, The Netherlands.,Radboudumc-CWZ Center of Expertise for Mycology, Nijmegen, The Netherlands
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5
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CRISPR-Cas9-Based Mutagenesis of the Mucormycosis-Causing Fungus Lichtheimia corymbifera. Int J Mol Sci 2020; 21:ijms21103727. [PMID: 32466287 PMCID: PMC7279233 DOI: 10.3390/ijms21103727] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2020] [Revised: 05/20/2020] [Accepted: 05/25/2020] [Indexed: 12/18/2022] Open
Abstract
Lichtheimia corymbifera is considered as one of the most frequent agents of mucormycosis. The lack of efficient genetic manipulation tools hampers the characterization of the pathomechanisms and virulence factors of this opportunistic pathogenic fungus. Although such techniques have been described for certain species, the performance of targeted mutagenesis and the construction of stable transformants have remained a great challenge in Mucorales fungi. In the present study, a plasmid-free CRISPR-Cas9 system was applied to carry out a targeted gene disruption in L. corymbifera. The described method is based on the non-homologous end-joining repair of the double-strand break caused by the Cas9 enzyme. Using this method, short, one-to-five nucleotide long-targeted deletions could be induced in the orotidine 5′-phosphate decarboxylase gene (pyrG) and, as a result, uracil auxotrophic strains were constructed. These strains are applicable as recipient strains in future gene manipulation studies. As we know, this is the first genetic modification of this clinically relevant fungus.
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6
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Dihydroorotate dehydrogenase inhibitors in anti-infective drug research. Eur J Med Chem 2019; 183:111681. [PMID: 31557612 DOI: 10.1016/j.ejmech.2019.111681] [Citation(s) in RCA: 46] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2019] [Revised: 08/01/2019] [Accepted: 09/05/2019] [Indexed: 01/08/2023]
Abstract
Pyrimidines are essential for the cell survival and proliferation of living parasitic organisms, such as Helicobacter pylori, Plasmodium falciparum and Schistosoma mansoni, that are able to impact upon human health. Pyrimidine building blocks, in human cells, are synthesised via both de novo biosynthesis and salvage pathways, the latter of which is an effective way of recycling pre-existing nucleotides. As many parasitic organisms lack pyrimidine salvage pathways for pyrimidine nucleotides, blocking de novo biosynthesis is seen as an effective therapeutic means to selectively target the parasite without effecting the human host. Dihydroorotate dehydrogenase (DHODH), which is involved in the de novo biosynthesis of pyrimidines, is a validated target for anti-infective drug research. Recent advances in the DHODH microorganism field are discussed herein, as is the potential for the development of DHODH-targeted therapeutics.
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7
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Singulani JL, Scorzoni L, de Oliveira HC, Marcos CM, Assato PA, Fusco-Almeida AM, Mendes-Giannini MJS. Applications of Invertebrate Animal Models to Dimorphic Fungal Infections. J Fungi (Basel) 2018; 4:jof4040118. [PMID: 30347646 PMCID: PMC6308930 DOI: 10.3390/jof4040118] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2018] [Revised: 10/15/2018] [Accepted: 10/16/2018] [Indexed: 02/07/2023] Open
Abstract
Dimorphic fungi can be found in the yeast form during infection and as hyphae in the environment and are responsible for a large number of infections worldwide. Invertebrate animals have been shown to be convenient models in the study of fungal infections. These models have the advantages of being low cost, have no ethical issues, and an ease of experimentation, time-efficiency, and the possibility of using a large number of animals per experiment compared to mammalian models. Invertebrate animal models such as Galleria mellonella, Caenorhabditis elegans, and Acanthamoebacastellanii have been used to study dimorphic fungal infections in the context of virulence, innate immune response, and the efficacy and toxicity of antifungal agents. In this review, we first summarize the features of these models. In this aspect, the growth temperature, genome sequence, availability of different strains, and body characteristics should be considered in the model choice. Finally, we discuss the contribution and advances of these models, with respect to dimorphic fungi Paracoccidioides spp., Histoplasma capsulatum, Blastomyces dermatitidis, Sporothrix spp., and Talaromyces marneffei (Penicillium marneffei).
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Affiliation(s)
- Junya L Singulani
- School of Pharmaceutical Sciences, São Paulo State University (UNESP), Araraquara, São Paulo 14800-903, Brazil.
| | - Liliana Scorzoni
- School of Pharmaceutical Sciences, São Paulo State University (UNESP), Araraquara, São Paulo 14800-903, Brazil.
| | - Haroldo C de Oliveira
- School of Pharmaceutical Sciences, São Paulo State University (UNESP), Araraquara, São Paulo 14800-903, Brazil.
| | - Caroline M Marcos
- School of Pharmaceutical Sciences, São Paulo State University (UNESP), Araraquara, São Paulo 14800-903, Brazil.
| | - Patricia A Assato
- School of Pharmaceutical Sciences, São Paulo State University (UNESP), Araraquara, São Paulo 14800-903, Brazil.
| | - Ana Marisa Fusco-Almeida
- School of Pharmaceutical Sciences, São Paulo State University (UNESP), Araraquara, São Paulo 14800-903, Brazil.
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8
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F901318 represents a novel class of antifungal drug that inhibits dihydroorotate dehydrogenase. Proc Natl Acad Sci U S A 2016; 113:12809-12814. [PMID: 27791100 DOI: 10.1073/pnas.1608304113] [Citation(s) in RCA: 161] [Impact Index Per Article: 20.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
There is an important medical need for new antifungal agents with novel mechanisms of action to treat the increasing number of patients with life-threatening systemic fungal disease and to overcome the growing problem of resistance to current therapies. F901318, the leading representative of a novel class of drug, the orotomides, is an antifungal drug in clinical development that demonstrates excellent potency against a broad range of dimorphic and filamentous fungi. In vitro susceptibility testing of F901318 against more than 100 strains from the four main pathogenic Aspergillus spp. revealed minimal inhibitory concentrations of ≤0.06 µg/mL-greater potency than the leading antifungal classes. An investigation into the mechanism of action of F901318 found that it acts via inhibition of the pyrimidine biosynthesis enzyme dihydroorotate dehydrogenase (DHODH) in a fungal-specific manner. Homology modeling of Aspergillus fumigatus DHODH has identified a predicted binding mode of the inhibitor and important interacting amino acid residues. In a murine pulmonary model of aspergillosis, F901318 displays in vivo efficacy against a strain of A. fumigatus sensitive to the azole class of antifungals and a strain displaying an azole-resistant phenotype. F901318 is currently in late Phase 1 clinical trials, offering hope that the antifungal armamentarium can be expanded to include a class of agent with a mechanism of action distinct from currently marketed antifungals.
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9
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Revisiting old friends: Developments in understanding Histoplasma capsulatum pathogenesis. J Microbiol 2016; 54:265-76. [DOI: 10.1007/s12275-016-6044-5] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2016] [Accepted: 02/02/2016] [Indexed: 12/27/2022]
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10
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Garfoot AL, Rappleye CA. Histoplasma capsulatum surmounts obstacles to intracellular pathogenesis. FEBS J 2015; 283:619-33. [PMID: 26235362 DOI: 10.1111/febs.13389] [Citation(s) in RCA: 49] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2015] [Revised: 07/25/2015] [Accepted: 07/27/2015] [Indexed: 11/28/2022]
Abstract
The fungal pathogen Histoplasma capsulatum causes respiratory and disseminated disease, even in immunocompetent hosts. In contrast to opportunistic pathogens, which are readily controlled by phagocytic cells, H. capsulatum yeasts are able to infect macrophages, survive antimicrobial defenses, and proliferate as an intracellular pathogen. In this review, we discuss some of the molecular mechanisms that enable H. capsulatum yeasts to overcome obstacles to intracellular pathogenesis. H. capsulatum yeasts gain refuge from extracellular obstacles such as antimicrobial lung surfactant proteins by engaging the β-integrin family of phagocytic receptors to promote entry into macrophages. In addition, H. capsulatum yeasts conceal immunostimulatory β-glucans to avoid triggering signaling receptors such as the β-glucan receptor Dectin-1. H. capsulatum yeasts counteract phagocyte-produced reactive oxygen species by expression of oxidative stress defense enzymes including an extracellular superoxide dismutase and an extracellular catalase. Within the phagosome, H. capsulatum yeasts block phagosome acidification, acquire essential metals such as iron and zinc, and utilize de novo biosynthesis pathways to overcome nutritional limitations. These mechanisms explain how H. capsulatum yeasts avoid and negate macrophage defense strategies and establish a hospitable intracellular niche, making H. capsulatum a successful intracellular pathogen of macrophages.
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Affiliation(s)
- Andrew L Garfoot
- Department of Microbiology, Department of Microbial Infection and Immunity, Ohio State University, Columbus, OH, USA
| | - Chad A Rappleye
- Department of Microbiology, Department of Microbial Infection and Immunity, Ohio State University, Columbus, OH, USA
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11
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Garfoot AL, Zemska O, Rappleye CA. Histoplasma capsulatum depends on de novo vitamin biosynthesis for intraphagosomal proliferation. Infect Immun 2014; 82:393-404. [PMID: 24191299 PMCID: PMC3911860 DOI: 10.1128/iai.00824-13] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2013] [Accepted: 10/29/2013] [Indexed: 01/07/2023] Open
Abstract
During infection of the mammalian host, Histoplasma capsulatum yeasts survive and reside within macrophages of the immune system. Whereas some intracellular pathogens escape into the host cytosol, Histoplasma yeasts remain within the macrophage phagosome. This intracellular Histoplasma-containing compartment imposes nutritional challenges for yeast growth and replication. We identified and annotated vitamin synthesis pathways encoded in the Histoplasma genome and confirmed by growth in minimal medium that Histoplasma yeasts can synthesize all essential vitamins with the exception of thiamine. Riboflavin, pantothenate, and biotin auxotrophs of Histoplasma were generated to probe whether these vitamins are available to intracellular yeasts. Disruption of the RIB2 gene (riboflavin biosynthesis) prevented growth and proliferation of yeasts in macrophages and severely attenuated Histoplasma virulence in a murine model of respiratory histoplasmosis. Rib2-deficient yeasts were not cleared from lung tissue but persisted, consistent with functional survival mechanisms but inability to replicate in vivo. In addition, depletion of Pan6 (pantothenate biosynthesis) but not Bio2 function (biotin synthesis) also impaired Histoplasma virulence. These results indicate that the Histoplasma-containing phagosome is limiting for riboflavin and pantothenate and that Histoplasma virulence requires de novo synthesis of these cofactor precursors. Since mammalian hosts do not rely on vitamin synthesis but instead acquire essential vitamins through diet, vitamin synthesis pathways represent druggable targets for therapeutics.
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Affiliation(s)
- Andrew L Garfoot
- Department of Microbiology, Department of Microbial Infection and Immunity, Ohio State University, Columbus, Ohio, USA
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12
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Use of uridine auxotrophy (ura3) for markerless transformation of the mycoinsecticide Beauveria bassiana. Appl Microbiol Biotechnol 2012; 97:3017-25. [DOI: 10.1007/s00253-012-4426-0] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2012] [Revised: 08/31/2012] [Accepted: 09/05/2012] [Indexed: 12/21/2022]
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13
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Berkes CA, Chan LLY, Wilkinson A, Paradis B. Rapid quantification of pathogenic fungi by Cellometer image-based cytometry. J Microbiol Methods 2012; 91:468-76. [PMID: 22985717 DOI: 10.1016/j.mimet.2012.09.008] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2012] [Revised: 09/08/2012] [Accepted: 09/09/2012] [Indexed: 11/19/2022]
Abstract
The objective of this study was to develop an image-based cytometric methodology for the quantification of viable pathogenic yeasts, which can offer increased sensitivity and efficiency when compared to the traditional colony forming unit (CFU) assay. Live/dead yeast quantification by flow cytometry has been previously demonstrated, however, adoption of flow cytometric detection of pathogenic yeasts has been limited for a number of practical reasons including its high cost and biosafety considerations. Our studies focus on detection of two human fungal pathogens: Histoplasma capsulatum and Candida albicans. H. capsulatum colonizes alveolar macrophages by replicating within the macrophage phagosome. Here, we quantitatively assess the growth of H. capsulatum yeasts within RAW 264.7 macrophages using acridine orange/propidium iodide staining in combination with Cellometer image-based cytometry; this method faithfully recapitulates growth trends as measured by traditional CFU enumeration, but with significantly increased sensitivity. Additionally, we directly assess infection of bone marrow-derived macrophages with a GFP-expressing strain of C. albicans. To demonstrate that image-based cytometry can be used as a tool to assess the susceptibility of fungi to antifungal drugs, we perform dose response experiments with the antifungal drugs amphotericin B and itraconazole and show that image-based cytometry allows rapid assessment of the kinetics of cytotoxicity induced by these antifungals. Our methodology offers a rapid, accurate, and economical means for detection and quantification of important human fungal pathogens, either alone or in association with host cells.
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AreA controls nitrogen source utilisation during both growth programs of the dimorphic fungus Penicillium marneffei. Fungal Biol 2011; 116:145-54. [PMID: 22208609 DOI: 10.1016/j.funbio.2011.10.009] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2011] [Revised: 10/28/2011] [Accepted: 10/28/2011] [Indexed: 12/17/2022]
Abstract
The opportunistic pathogen Penicillium marneffei displays a temperature-dependent dimorphic switching program with saprophytic hyphal growth at 25 °C and yeast growth at 37 °C. The areA gene of P. marneffei has been isolated and found to be required for the utilisation of nonpreferred nitrogen sources during both growth programs of P. marneffei, albeit to differing degrees. Based on this functional characterisation and high degree of sequence conservation with other fungal GATA factors, P. marneffei areA represents an orthologue of Aspergillus nidulans areA and Neurospora crassa NIT2. Based on this study it is proposed that AreA is likely to contribute to the pathogenicity of P. marneffei by facilitating growth in the host environment and regulating the expression of potential virulence factors such as extracellular proteases.
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González-González AE, Taylor ML, Curiel-Quesada E. [Relevant aspects of the Hcp100 molecular marker of Histoplasma capsulatum and its potential therapeutic use in histoplasmosis]. Rev Iberoam Micol 2011; 29:115-9. [PMID: 22037114 DOI: 10.1016/j.riam.2011.09.001] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2011] [Revised: 09/25/2011] [Accepted: 09/30/2011] [Indexed: 10/15/2022] Open
Abstract
BACKGROUND Fungal pathogens have developed strategies, involving genes expression that favors their persistence and multiplication in the host. The absence of molecules encoded by these genes could interfere with the growth and death of these fungi. In the past, a coactivator protein coding gene (Hcp100) of the fungus Histoplasma capsulatum was reported, which is overexpressed after 1h of contact between fungal yeast-cells and murine macrophages. The product of this gene, a protein of 100 kDa (Hcp100) of H. capsulatum, is probably a regulatory protein involved in the processes required for fungal adaptation and its survival in the intracellular hostile conditions of the macrophages. A 210-bp fragment of the Hcp100 marker has proved to be an excellent tool for H. capsulatum molecular detection in clinical samples. The potential use of this gene as a therapeutic target in Plasmodium falciparum has been explored through the inhibition of both, the gene and the protein p100 of the parasite, by blocking its growth. METHODS Based on the above mentioned antecedents, we believe that the Hcp100 has an important role in the development and maintenance of the H. capsulatum yeast cells within macrophages. RESULTS AND CONCLUSIONS To study the probable function of Hcp100 in the yeast-phase of this fungal pathogen is relevant to understand its activity and to propose it as a therapeutic target for histoplasmosis treatment.
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Affiliation(s)
- Antonio Ernesto González-González
- Departamento de Microbiología y Parasitología, Facultad de Medicina, Universidad Nacional Autónoma de México, México DF, México. skapunking
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Secreted dipeptidyl peptidase IV activity in the dimorphic fungal pathogen Histoplasma capsulatum. Infect Immun 2009; 77:2447-54. [PMID: 19349421 DOI: 10.1128/iai.01345-08] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Dipeptidyl peptidase type IV (DppIV) enzymes are broadly distributed phylogenetically and display diverse functions, including intercellular signaling, immunomodulation, protein maturation and processing, metabolism, and nutrient acquisition. We identified a secreted proteolytic activity in Histoplasma capsulatum effective toward DppIV-specific substrates. In order to determine the gene(s) that encodes this activity, we identified two putative DPPIV homologs (HcDPPIVA and HcDPPIVB) in H. capsulatum based on a homology search with Aspergillus fumigatus DppIV. Comparative sequence analysis revealed that HcDppIVA is similar to secreted DppIV enzymes, while HcDppIVB clusters with intracellular DapB-like enzymes. Unexpectedly, silencing of HcDPPIVA by RNA interference (RNAi) had no effect on secreted DppIV activity and an HcDPPIVA-null deletion mutant also showed no abrogation of secreted DppIV activity. In contrast, RNAi silencing of HcDPPIVB significantly reduced the level of secreted DppIV activity. RNAi silencing of HcDPPIVB in the HcDPPIVA-null mutant had no additional effect on secreted DppIV activity, indicating that HcDPPIVA does not contribute to secreted activity. RNAi silencing of HcDPPIVB did not affect the ability to kill a murine macrophage-like cell line, RAW 264.7, indicating that this gene is not required for infection of macrophages.
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Costa M, Borges CL, Bailão AM, Meirelles GV, Mendonça YA, Dantas SFIM, de Faria FP, Felipe MSS, Molinari-Madlum EEWI, Mendes-Giannini MJS, Fiuza RB, Martins WS, Pereira M, Soares CMA. Transcriptome profiling of Paracoccidioides brasiliensis yeast-phase cells recovered from infected mice brings new insights into fungal response upon host interaction. MICROBIOLOGY-SGM 2008; 153:4194-4207. [PMID: 18048933 DOI: 10.1099/mic.0.2007/009332-0] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Paracoccidioides brasiliensis is a fungal human pathogen with a wide distribution in Latin America. It causes paracoccidioidomycosis, the most widespread systemic mycosis in Latin America. Although gene expression in P. brasiliensis had been studied, little is known about the genome sequences expressed by this species during the infection process. To better understand the infection process, 4934 expressed sequence tags (ESTs) derived from a non-normalized cDNA library from P. brasiliensis (isolate Pb01) yeast-phase cells recovered from the livers of infected mice were annotated and clustered to a UniGene (clusters containing sequences that represent a unique gene) set with 1602 members. A large-scale comparative analysis was performed between the UniGene sequences of P. brasiliensis yeast-phase cells recovered from infected mice and a database constructed with sequences of the yeast-phase and mycelium transcriptome (isolate Pb01) (https://dna.biomol.unb.br/Pb/), as well as with all public ESTs available at GenBank, including sequences of the P. brasiliensis yeast-phase transcriptome (isolate Pb18) (http://www.ncbi.nlm.nih.gov/). The focus was on the overexpressed and novel genes. From the total, 3184 ESTs (64.53%) were also present in the previously described transcriptome of yeast-form and mycelium cells obtained from in vitro cultures (https://dna.biomol.unb.br/Pb/) and of those, 1172 ESTs (23.75% of the described sequences) represented transcripts overexpressed during the infection process. Comparative analysis identified 1750 ESTs (35.47% of the total), comprising 649 UniGene sequences representing novel transcripts of P. brasiliensis, not previously described for this isolate or for other isolates in public databases. KEGG pathway mapping showed that the novel and overexpressed transcripts represented standard metabolic pathways, including glycolysis, amino acid biosynthesis, lipid and sterol metabolism. The unique and divergent representation of transcripts in the cDNA library of yeast cells recovered from infected mice suggests differential gene expression in response to the host milieu.
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Affiliation(s)
- Milce Costa
- Laboratório de Biologia Molecular, Instituto de Ciências Biológicas, Universidade Federal de Goiás, 74001-970, Goiânia, Goiás, Brazil
| | - Clayton L Borges
- Laboratório de Biologia Molecular, Instituto de Ciências Biológicas, Universidade Federal de Goiás, 74001-970, Goiânia, Goiás, Brazil
| | - Alexandre M Bailão
- Laboratório de Biologia Molecular, Instituto de Ciências Biológicas, Universidade Federal de Goiás, 74001-970, Goiânia, Goiás, Brazil
| | - Gabriela V Meirelles
- Laboratório de Biologia Molecular, Instituto de Ciências Biológicas, Universidade Federal de Goiás, 74001-970, Goiânia, Goiás, Brazil
| | - Yuri A Mendonça
- Laboratório de Biologia Molecular, Instituto de Ciências Biológicas, Universidade Federal de Goiás, 74001-970, Goiânia, Goiás, Brazil
| | - Sabrina F I M Dantas
- Laboratório de Biologia Molecular, Instituto de Ciências Biológicas, Universidade Federal de Goiás, 74001-970, Goiânia, Goiás, Brazil
| | - Fabrícia P de Faria
- Laboratório de Biologia Molecular, Instituto de Ciências Biológicas, Universidade Federal de Goiás, 74001-970, Goiânia, Goiás, Brazil
| | - Maria S S Felipe
- Laboratório de Biologia Molecular, Universidade de Brasília, Brasília, Brazil
| | | | - Maria J S Mendes-Giannini
- Laboratório de Micologia, Universidade Estadual Júlio de Mesquita Filho, Araraquara, São Paulo, Brazil
| | - Rogério B Fiuza
- Laboratório de Biologia Molecular, Instituto de Ciências Biológicas, Universidade Federal de Goiás, 74001-970, Goiânia, Goiás, Brazil
| | | | - Maristela Pereira
- Laboratório de Biologia Molecular, Instituto de Ciências Biológicas, Universidade Federal de Goiás, 74001-970, Goiânia, Goiás, Brazil
| | - Célia M A Soares
- Laboratório de Biologia Molecular, Instituto de Ciências Biológicas, Universidade Federal de Goiás, 74001-970, Goiânia, Goiás, Brazil
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Bohse ML, Woods JP. RNA interference-mediated silencing of the YPS3 gene of Histoplasma capsulatum reveals virulence defects. Infect Immun 2007; 75:2811-7. [PMID: 17403872 PMCID: PMC1932869 DOI: 10.1128/iai.00304-07] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The YPS3 gene of Histoplasma capsulatum encodes a protein that is both surface localized in the cell wall of H. capsulatum and released into the culture medium. This protein is produced only during the pathogenic yeast phase of infection and is also expressed differentially in H. capsulatum strains of different virulence levels. In this study, we silenced the YPS3 transcript by using an interfering-RNA strategy and examined the silenced mutants for phenotypic differences in vitro and during infection. The mutants showed no growth defect during in vitro culture in a defined medium at 37 degrees C and appeared to have normal virulence in a RAW 264.7 murine macrophage-like cell line. In a C57BL/6 mouse model of infection, however, the mutants caused significantly decreased fungal burdens, particularly in the peripheral phagocyte-rich tissues of livers and spleens. This defect in organ colonization was evident within 3 days of infection; however, it appeared to be exacerbated at later time points.
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Affiliation(s)
- Megan L Bohse
- Department of Medical Microbiology and Immunology, 420 SMI, University of Wisconsin Medical School, 1300 University Avenue, Madison, WI 53706, USA
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Bohse ML, Woods JP. Expression and interstrain variability of the YPS3 gene of Histoplasma capsulatum. EUKARYOTIC CELL 2007; 6:609-15. [PMID: 17337639 PMCID: PMC1865658 DOI: 10.1128/ec.00010-07] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The YPS3 locus of the dimorphic fungus Histoplasma capsulatum encodes a secreted and surface-localized protein specific to the pathogenic yeast phase. In this study we examined this locus in 32 H. capsulatum strains and variants. Although protein production is limited to a select group of strains, the North American restriction fragment length polymorphism class 2/NAm 2 isolates, the locus was present in all the strains we examined. The YPS3 gene is well conserved in its 5' and 3' regions but displays an intragenic hypervariable region of tandem repeats that fluctuates in size between strains. This feature is similar to that seen with genes encoding several cell surface proteins in other fungi.
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Affiliation(s)
- Megan L Bohse
- Department of Medical Microbiology and Immunology, 420 SMI, University of Wisconsin Medical School, 1300 University Avenue, Madison, WI 53706, USA
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20
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Marion CL, Rappleye CA, Engle JT, Goldman WE. An alpha-(1,4)-amylase is essential for alpha-(1,3)-glucan production and virulence in Histoplasma capsulatum. Mol Microbiol 2006; 62:970-83. [PMID: 17038119 DOI: 10.1111/j.1365-2958.2006.05436.x] [Citation(s) in RCA: 91] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Histoplasma capsulatum is a dimorphic fungus that causes respiratory and systemic disease and is capable of surviving and replicating within macrophages. The virulence of Histoplasma has been linked to cell wall alpha-(1,3)-glucan; however, the role of this polysaccharide during infection, its organization within the cell wall, and its synthesis and regulation remain poorly understood. To identify genes involved in the biosynthesis of alpha-(1,3)-glucan, we employed a forward genetics strategy to isolate physically marked mutants with reduced alpha-(1,3)-glucan. Insertional mutants were generated in a virulent strain of H. capsulatum by optimization of Agrobacterium tumefaciens-mediated transformation. Approximately 90% of these mutants possessed single insertions with no chromosomal rearrangements or deletions in the host genome. To confirm the role and specificity of identified candidate genes, we phenocopied the disrupted locus by either RNA interference or targeted gene deletion. Our findings indicate alpha-(1,3)-glucan production requires the function of the AMY1 gene product, a novel protein with homology to the alpha-amylase family of glycosyl hydrolases, and UGP1, a UTP-glucose-1-phosphate uridylyltransferase which synthesizes UDP-glucose monomers. Loss of AMY1 function attenuated the ability of Histoplasma to kill macrophages and to colonize murine lungs.
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Affiliation(s)
- Christopher L Marion
- Department of Molecular Microbiology, Washington University, St Louis, MO 63110, USA
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21
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Abstract
Most dimorphic fungal pathogens cause respiratory disease in mammals and must therefore possess virulence mechanisms to combat and overcome host pulmonary defenses. Over the past decade, advances in genetic tools have made it possible to investigate the basis of dimorphic fungal pathogenesis at the molecular level. Gene disruptions and RNA interference have now formally demonstrated the involvement of six virulence factors: CBP, alpha-(1,3)-glucan, BAD1, SOWgp, Mep1, and urease. Additional candidate virulence-associated genes have been identified on the premise that factors necessary for pathogenicity are associated specifically with the parasitic form. This principle continues to form the foundation for genomics-based analyses to further augment the list. Thus, the stage is set and the tools are in place for the next phase of medical mycology research: defining the virulence-associated factors underlying the success of dimorphic fungal pathogens.
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Affiliation(s)
- Chad A Rappleye
- Department of Microbiology, Ohio State University, Columbus, Ohio 43210, USA.
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22
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Abstract
Aspergillus fumigatus is a ubiquitous fungus that plays an important role in carbon and nitrogen recycling in nature. Because A. fumigatus is thermotolerant, it is a predominant organism during the high-temperature phase of the compost cycle. The ability to grow at elevated temperatures and to utilize numerous varied sources of both carbon and nitrogen to support its growth have made A. fumigatus an important opportunistic pathogen of humans as well as a vital part of the nutrient-recycling ecosystem. Data correlating the growth rate and germination potential of A. fumigatus at 37 degrees C with its pathogenic potential suggest that these are related, both when viewed from a population standpoint and when analyzed on a single gene basis. Nutritional versatility has been cited as an important contributor to virulence as well. Indeed, perturbation of pathways involved with nitrogen or carbon sensing has been shown to reduce virulence in animal models, even when in vitro growth rates have not been altered. Therefore, the remarkable ability of A. fumigatus to grow efficiently under a variety of environmental conditions and to utilize a wide variety of substrates to meet its nutritional needs contributes to its role as the predominant mould pathogen of immunocompromised patients.
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Affiliation(s)
- Judith C Rhodes
- Department of Pathology and Laboratory Medicine, University of Cincinnati, Cincinnati, Ohio 45267-0529, USA.
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23
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Rooney PJ, Klein BS. Sequence elements necessary for transcriptional activation of BAD1 in the yeast phase of Blastomyces dermatitidis. EUKARYOTIC CELL 2005; 3:785-94. [PMID: 15189999 PMCID: PMC420126 DOI: 10.1128/ec.3.3.785-794.2004] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Blastomyces dermatitidis is a dimorphic fungal pathogen that converts from mycelia or conidia to a host-adapted yeast morphotype upon infection. Conversion to the yeast form is accompanied by the production of the virulence factor BAD1. Yeast-phase-specific expression of BAD1 is transcriptionally regulated, and its promoter shares homology with that of the yeast-phase-specific gene YPS3 of Histoplasma capsulatum. Serial truncations of the BAD1 upstream region were fused to the lacZ reporter to define functional areas in the promoter. Examination of PBAD1-lacZ fusions in B. dermatitidis indicated that BAD1 transcription is upregulated in the yeast phase. The 63-nucleotide box A region conserved in the YPS3 upstream region was shown to be an essential component of the minimal BAD1 promoter. A matched PYPS3-lacZ construct indicated that this same region was needed for minimal YPS3 promoter activity in B. dermatitidis transformants. Reporter activity in H. capsulatum transformants similarly showed a requirement for box A in the minimal BAD1 promoter. Several putative transcription factor binding sites were identified within box A of BAD1. Replacement of two of these predicted sites within box A--a cAMP responsive element and a Myb binding site--sharply reduced transcriptional activity, indicating that these regions are critical in dictating the yeast-phase-specific expression of this crucial virulence determinant of B. dermatitidis.
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Affiliation(s)
- Peggy J Rooney
- Department of Medical Microbiology and Immunology, University of Wisconsin Medical School, Madison, WI 53792, USA
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24
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Abstract
Histoplasma capsulatum is a significant respiratory and systemic fungal pathogen. Although many molecular tools have been developed, the fulfillment of Koch's postulates to determine gene function has been hampered by obstacles to homologous gene targeting. Because H. capsulatum displays a considerable array of virulence mechanisms and has a 40-Mb genome that is currently being sequenced, the capability to perform high-throughput molecular manipulations would clearly be beneficial. Recent demonstration and application of experimental RNA interference (RNAi) technology promises a major contribution to advances in this area.
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Affiliation(s)
- Jon P Woods
- Department of Medical Microbiology & Immunology, University of Wisconsin Medical School, 1300 University Avenue, 420 SMI, Madison, Wisconsin 53706-1532 WI, USA.
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25
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Rappleye CA, Engle JT, Goldman WE. RNA interference in Histoplasma capsulatum demonstrates a role for alpha-(1,3)-glucan in virulence. Mol Microbiol 2004; 53:153-65. [PMID: 15225311 DOI: 10.1111/j.1365-2958.2004.04131.x] [Citation(s) in RCA: 188] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Histoplasma capsulatum is a fungal pathogen that causes respiratory and systemic disease by proliferating within macrophages. While much is known about histoplasmosis, only a single virulence factor has been defined, in part because of the inefficiency of Histoplasma reverse genetics. As an alternative to allelic replacement, we have developed a telomeric plasmid-based system for silencing gene expression in Histoplasma by RNA interference (RNAi). Episomal expression of long RNAs that form stem-loop structures triggered gene silencing. To test the effectiveness of RNAi in Histoplasma, we depleted expression of a gfp transgene as well as two endogenous genes, ADE2 and URA5, and showed significant reductions in corresponding gene function. Silencing was target gene specific, stable during macrophage infection and reversible. We used RNAi targeting AGS1 (encoding alpha-(1,3)-glucan synthase) to deplete levels of alpha-(1,3)-glucan, a cell wall polysaccharide. Loss of alpha-(1,3)-glucan by RNAi yielded phenotypes indistinguishable from an AGS1 deletion: attenuation of the ability to kill macrophages and colonize murine lungs. This demonstrates for the first time that alpha-(1,3)-glucan is an important contributor to Histoplasma virulence.
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Affiliation(s)
- Chad A Rappleye
- Department of Molecular Microbiology, Campus Box 8230, Washington University, St Louis, MO 63110, USA
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Ignatov A, Keath EJ. Molecular cell biology and molecular genetics of Histoplasma capsulatum. Int J Med Microbiol 2002; 292:349-61. [PMID: 12452281 DOI: 10.1078/1438-4221-00218] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Histoplasma capsulatum is a dimorphic ascomycete which is capable of producing a broad spectrum of disease ranging from mild asymptomatic, pulmonary illness to severe, life-threatening systemic mycosis. Regulatory mechanisms that use temperature and other environmental cues are paramount to the successful adaptation of the organism as an effective intracellular pathogenic yeast. Although the biochemistry and phenomenology of reversible morphogenesis have been well examined in Histoplasma, the identification and functional characterization of genes and their products that are required for early establishment or maintenance of the parasitic yeast phase in intracellular host compartments have only recently been fruitful. Advances in the molecular biology of Histoplasma, including approaches to introduce telomeric plasmids, reporter fusion constructs, and gene disruption cassettes into the fungus are poised to solidify the pre-eminence of this fungus as a model system which can be applied to other dimorphic fungal pathogens that exhibit similar cellular and immunological complexities. This review centers on recent developments in the molecular cell biology and molecular genetics of Histoplasma capsulatum that provide important new avenues for examining the mold-to-yeast phase transition beyond the historical, binary view of dimorphism and the implications that these successful approaches may have on seminal issues in fungal pathogenesis.
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Affiliation(s)
- Atanas Ignatov
- Department of Biology, Saint Louis University, 3507 Laclede Avenue, St. Louis, MO 63103, USA
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27
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Woods JP. Histoplasma capsulatum molecular genetics, pathogenesis, and responsiveness to its environment. Fungal Genet Biol 2002; 35:81-97. [PMID: 11848673 DOI: 10.1006/fgbi.2001.1311] [Citation(s) in RCA: 76] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Histoplasma capsulatum is a thermally dimorphic ascomycete that is a significant cause of respiratory and systemic disease in mammals including humans, especially immunocompromised individuals such as AIDS patients. As an environmental mold found in the soil, it is a successful member of a competitive polymicrobial ecosystem. Its host-adapted yeast form is a facultative intracellular pathogen of mammalian macrophages. H. capsulatum faces a variety of environmental changes during the course of infection and must survive under harsh conditions or modulate its microenvironment to achieve success as a pathogen. Histoplasmosis may be considered the fungal homolog of the bacterial infection tuberculosis, since both H. capsulatum and Mycobacterium tuberculosis exploit the macrophage as a host cell and can cause acute or persistent pulmonary and disseminated infection and reactivation disease. The identification and functional analysis of biologically or pathogenically important H. capsulatum genes have been greatly facilitated by the development of molecular genetic experimental capabilities in this organism. This review focuses on responsiveness of this fungus to its environment, including differential expression of genes and adaptive phenotypic traits.
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Affiliation(s)
- Jon P Woods
- Department of Medical Microbiology & Immunology, University of Wisconsin Medical School, Madison, Wisconsin 53706-1532, USA
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Abstract
Sophisticated molecular biological research has revealed many virulence attributes in at least four pathogenic fungi, but the future study of fungal virulence requires investigators to distinguish between molecules that directly interact with the host, molecules that regulate these, and molecules that are always required for fungal growth and survival, independent of the host.
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Affiliation(s)
- F C Odds
- Department of Molecular and Cell Biology, University of Aberdeen, Institute of Medical Sciences, Aberdeen, AB25 2ZD, UK.
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Kügler S, Young B, Miller VL, Goldman WE. Monitoring phase-specific gene expression in Histoplasma capsulatum with telomeric GFP fusion plasmids. Cell Microbiol 2000; 2:537-47. [PMID: 11207606 DOI: 10.1046/j.1462-5822.2000.00078.x] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Dimorphism is an essential feature of Histoplasma capsulatum pathogenesis, and much attention has been focused on characteristics that are unique to the saprophytic mycelial phase or the parasitic yeast phase. Recently, we identified a secreted calcium-binding protein, CBP, that is produced in large amounts by yeast cells but is undetectable in mycelial cultures. In this study, the green fluorescent protein (GFP) was established as a reporter in H. capsulatum to study regulation of CBP1 expression in cultures and in single cells grown under different conditions and inside macrophages. One GFP version that was optimized for human codon usage yielded highly fluorescent Histoplasma yeast cells. By monitoring GFP fluorescence during the transition from mycelia to yeast, we demonstrated that the CBP1 promoter is only fully active after complete morphological conversion to the yeast form, indicating for the first time that CBP1 is developmentally regulated rather than simply temperature regulated. Continuous activity of the CBP1 promoter during infection of macrophages supports the hypothesis that CBP secretion plays an important role for Histoplasma survival within the phagolysosome. Broth cultures of Histoplasma yeasts carrying a CBP-GFP protein fusion construct were able to secrete a full-length fluorescent fusion protein that remained localized within the phagolysosomes of infected macrophages. Additionally, a comparison of two Histoplasma strains carrying the CBP1 promoter fusion construct either epichromosomally or integrated into the chromosome revealed cell-to-cell variation in plasmid copy number due to uneven plasmid partitioning into daughter cells.
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Affiliation(s)
- S Kügler
- Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, MO 63110, USA
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Sebghati TS, Engle JT, Goldman WE. Intracellular parasitism by Histoplasma capsulatum: fungal virulence and calcium dependence. Science 2000; 290:1368-72. [PMID: 11082066 DOI: 10.1126/science.290.5495.1368] [Citation(s) in RCA: 134] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Histoplasma capsulatum is an effective intracellular parasite of macrophages and causes the most prevalent fungal respiratory disease in the United States. A "dimorphic" fungus, H. capsulatum exists as a saprophytic mold in soil and converts to the parasitic yeast form after inhalation. Only the yeasts secrete a calcium-binding protein (CBP) and can grow in calcium-limiting conditions. To probe the relation between calcium limitation and intracellular parasitism, we designed a strategy to disrupt CBP1 in H. capsulatum using a telomeric linear plasmid and a two-step genetic selection. The resultingcbp1 yeasts no longer grew when deprived of calcium, and they were also unable to destroy macrophages in vitro or proliferate in a mouse model of pulmonary infection.
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Affiliation(s)
- T S Sebghati
- Department of Molecular Microbiology, Campus Box 8230, Washington University School of Medicine, St. Louis, MO 63110, USA
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Fisher KL, Woods JP. Determination of beta-glucosidase enzymatic function of the histoplasma capsulatum H antigen using a native expression system. Gene 2000; 247:191-7. [PMID: 10773459 DOI: 10.1016/s0378-1119(00)00099-8] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The Histoplasma capsulatum H antigen is a major secreted glycoprotein of this pathogenic fungus that is a target of humoral and cell-mediated host responses. Its predicted protein sequence displays homology to beta-glucosidases of other organisms, but a recombinant antigen expressed in a prokaryotic system showed no enzymatic activity. We expressed a recombinant form of the protein carrying a carboxyl-terminus oligohistidine tag in the native fungal background to facilitate proper glycosylation and folding of a product that could then be purified from culture supernatants using nickel affinity chromatography. The recombinant protein was expressed and secreted by a transformant carrying the modified gene under the control of its native promoter. The purified protein from the native expression system showed beta-glucosidase enzymatic activity in substrate gels and quantitative microplate assays. This activity was blocked by glucosidase-specific inhibitors. These results are the first direct demonstration of the function of this protein, and show the utility of expression in a native system to achieve post-translational modification necessary for structural and functional integrity.
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Affiliation(s)
- K L Fisher
- University of Wisconsin Medical School, Department of Medical Microbiology and Immunology, Madison, WI 53706-1532, USA
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32
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Retallack DM, Deepe GS, Woods JP. Applying in vivo expression technology (IVET) to the fungal pathogen Histoplasma capsulatum. Microb Pathog 2000; 28:169-82. [PMID: 10702358 DOI: 10.1006/mpat.1999.0337] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Understanding how pathogens survive within the host cell is of paramount importance in the development of vaccines and therapeutic agents. This task has been particularly daunting in the study of fungal pathogens due to the lack of easily manipulated genetic systems. In recent years several molecular genetic reporter systems have been developed to identify genes expressed during the infection process and potential virulence determinants. The development of one method in particular, in vivo expression technology (IVET), has led to the discovery of several genes from various bacterial pathogens necessary for survival during infection. The recent development of molecular genetic tools for Histoplasma capsulatum has enabled us to adapt the IVET technology for this pathogenic fungus utilizing the URA5 gene, which is essential for H. capsulatum survival in mice and in cultured macrophages, as a reporter of in vivo gene expression. We report the first successful application of IVET screening of a fungal pathogen for genes expressed exclusively during infection.
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Affiliation(s)
- D M Retallack
- Department of Medical Microbiology and Immunology, University of Wisconsin Medical School, Madison, WI 53706, USA
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33
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Retallack DM, Woods JP. Molecular epidemiology, pathogenesis, and genetics of the dimorphic fungus Histoplasma capsulatum. Microbes Infect 1999; 1:817-25. [PMID: 10816087 DOI: 10.1016/s1286-4579(99)80084-7] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
Histoplasma capsulatum, the causative agent of the most common systemic fungal infection, histoplasmosis, has become subject to increasing study in parallel with rising prevalence of human immunodeficiency. This review presents a summary of the advances made in the investigation of H. capsulatum genomics, molecular epidemiology, pathogenesis, and molecular genetics.
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Affiliation(s)
- D M Retallack
- Department of Medical Microbiology and Immunology, University of Wisconsin Medical School, Madison 53706, USA
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34
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Fisher KL, Deepe GS, Woods JP. Histoplasma capsulatum strain variation in both H antigen production and beta-glucosidase activity and overexpression of HAG1 from a telomeric linear plasmid. Infect Immun 1999; 67:3312-6. [PMID: 10377107 PMCID: PMC116512 DOI: 10.1128/iai.67.7.3312-3316.1999] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The H antigen of the dimorphic fungal pathogen Histoplasma capsulatum was first described over 40 years ago. It is a secreted glycoprotein that is immunogenic during infection. Recent cloning of the H antigen gene (HAG1) indicated sequence homology with genes for fungal beta-glucosidases. To understand the biological role of this immunodominant antigen in H. capsulatum, enzymatic assays were performed to determine whether H. capsulatum contained a beta-glucosidase enzyme activity and whether this activity was encoded by the HAG1 gene. Substrate gels with H. capsulatum culture supernatants revealed beta-glucosidase activity near the predicted mobility of the H antigen. Quantitative microtiter plate assays revealed marked differences in secreted beta-glucosidase activities from three H. capsulatum restriction fragment length polymorphism (RFLP) classes, with RFLP class II strains displaying high levels of enzyme activity, in contrast to the low levels of activity exhibited by class I and III strains. Immunoblotting of culture supernatants with an H antigen-specific antiserum demonstrated differences in H protein expression levels between the H. capsulatum classes, with a correlation between secreted enzyme activity and H protein levels. We took advantage of these class differences to demonstrate multicopy plasmid H gene overexpression by transformation of an HAG1 plasmid into H. capsulatum. Both a class II strain (G217Bura5-23) and a class III strain (G184ASura5-11) transformed with the telomeric overexpression plasmid pMAD401 displayed increased levels of beta-glucosidase enzyme activity and H protein expression compared to the levels in control transformants containing only the single genomic copy of HAG1. This is the first demonstration of telomeric plasmid-mediated protein overexpression in this pathogenic fungus, and the findings support the identification of the H antigen as a beta-glucosidase.
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Affiliation(s)
- K L Fisher
- Department of Medical Microbiology and Immunology, University of Wisconsin Medical School, Madison, Wisconsin 53706, USA
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Abstract
The isolation of auxotrophic markers is important for molecular genetic studies of the dimorphic fungus Histoplasma capsulatum. We have isolated a UV-induced mutant of H. capsulatum, resulting in nonreverting uracil auxotrophy due to a mutation in the URA5 gene. In this study, we show that this mutation is a GG to TA conversion bordering the 5' donor splice site of intron 2. The mutation results in the lack of splicing of intron 2 from the URA5 transcript, and subsequently premature termination of the peptide. This study is the first showing that consensus Group II intron sequences are both utilized and essential for functional expression of a gene in H. capsulatum.
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Affiliation(s)
- D M Retallack
- University of Wisconsin Medical School, Department of Medical Microbiology and Immunology, Madison, WI, USA
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